Iodine-Containing Heterocyclic Organic Compounds: Basic Concepts, Structural Types, Application Areas, and Product Selection Guide (with Product Tables 1–4)

I. Introduction

In modern organic chemistry, medicinal chemistry, radiotracer studies, and functional molecule research, heterocycles are among the most frequently encountered molecular scaffolds. Once iodine is introduced into a heterocyclic framework, the molecule often acquires two important sets of characteristics at the same time: one derives from iodine itself, including reactivity, polarizability, and labelability; the other derives from the heterocycle, including electronic effects, coordination ability, and structural diversity. For this reason, such compounds appear not only in synthetic methodology, but also in nuclear medicine, molecular recognition, and hypervalent iodine chemistry.

It should be noted that the term “iodine-containing heterocyclic organic compounds” as used in this article adopts a practical, application-oriented scope. It does not refer narrowly to heterocycles in which iodine itself is one of the ring-forming atoms. Rather, it broadly refers to organic compounds that contain both a heterocyclic unit and iodine-related structural features. This article focuses on two major classes: one consists of ordinary iodinated heterocycles bearing a covalent C–I bond on the heterocyclic scaffold; the other consists of cyclic hypervalent iodine heterocyclic or pseudocyclic systems represented by benziodoxole, benziodoxolone, and benziodazolone. The former more commonly serve as substrates, synthetic intermediates, probes, or precursors for radiolabeling, whereas the latter are more commonly used in oxidation, group-transfer, and catalysis-related methodology.

Category	Key structural feature	Representative forms	Common roles in research
Ordinary iodinated heterocyclic compounds	Covalent C–I bond on a heterocyclic scaffold	Iodopyridines, iodoimidazoles, iodoindoles, iodinated benzotriazoles, iodinated nucleosides/nucleobase analogs, etc.	Substrates, synthetic intermediates, radiolabeling precursors, molecular probes
Cyclic hypervalent iodine heterocyclic compounds	Iodine is in a high oxidation state such as I(III) / I(V) and is stabilized by a ring system	Benziodoxole, benziodazolone, and benziodazole families	Oxidants, group-transfer reagents, halogen-bond donors, catalytic precursors

II. What Are “Iodine-Containing Heterocyclic Organic Compounds”?

From the scope of this article, “iodine-containing heterocyclic organic compounds” are not a single structural class, but rather an application-oriented umbrella concept that includes both ordinary iodinated heterocycles and cyclic hypervalent iodine heterocyclic or pseudocyclic systems.

Term	Core meaning	Key point for understanding
Organic	Molecular systems based on carbon frameworks	Indicates that these molecules fall within the scope of organic chemistry
Iodine	The molecule contains iodine	Iodine can impart relatively high reactivity, labeling value, and, in some systems, halogen-bonding or hypervalent iodine characteristics
Heterocycle	A ring containing ring-forming atoms other than carbon, commonly N, O, or S	Common heterocycles include pyridine, imidazole, indole, furan, thiophene, thiazole, etc.
Compound	A specific molecule with a defined composition and structure	Emphasizes that the discussion concerns concrete molecules rather than isolated elements or abstract concepts
Iodine-containing heterocyclic organic compounds	A class of compounds based on organic molecules that contain a heterocyclic scaffold and also contain iodine	In common synthetic and medicinal-chemistry applications, the focus is usually on heterocyclic compounds bearing a C–I bond; in a broader sense, it also includes cyclic hypervalent iodine systems in which the hypervalent iodine center is stabilized in a heterocyclic form

III. Why These Iodine-Containing Heterocyclic Organic Compounds Are Worth Understanding

Key point	Brief explanation	Practical significance for research or experiments
Not a simple sum of “iodine + heterocycle”	Iodine can provide relatively high reactivity, labeling value, and halogen-bonding potential; heterocycles provide electronic tuning, recognition features, and scaffold diversity	These molecules often combine the properties of both a “structural unit” and a “functional interface”
Ordinary iodinated heterocycles are often high-value synthetic intermediates	Iodinated (hetero)arenes are commonly used in organic synthesis as intermediates that can be transformed further	Suitable for cross-coupling, post-functionalization, and extension of multistep routes
These molecules are naturally suited to “post-ring-construction elaboration”	An iodinated heterocycle can be either the product of ring construction or a downstream transformation site	Helps improve continuity and modularity in route design
Some can be used for radiolabeling and tracing	Once radioactive iodine isotopes are introduced, these molecules can be used in imaging, therapeutic research, or pharmacokinetic tracing	Of special value in nuclear medicine and molecular probe research
Hypervalent iodine heterocycles expand their utility as tools	Some cyclic hypervalent iodine heterocycles are not ordinary substrates, but platforms for oxidation, group transfer, or catalysis	This makes such compounds not only research objects but also direct reaction tools
Application scenarios span multiple directions	Relevant research covers organic synthesis, medicinal chemistry, nuclear medicine, halogen-bond catalysis, and supramolecular chemistry	This shows that they are not a fringe concept, but a cross-disciplinary molecular family with both methodological and application value

IV. What Types Are Commonly Included in This Class of Compounds?

4.1 Ordinary Iodinated Heterocyclic Compounds

This category refers to compounds in which an iodine substituent is directly attached to a heterocyclic scaffold, usually in the form of a C–I bond. They may be monocyclic heteroarenes or fused heterocycles, and the heteroatoms most commonly involved are N, O, and S. Typical structures include iodopyridines, iodoimidazoles, iodoindoles, iodothiophenes, iodinated benzotriazoles, and iodoimidazopyridines. A large body of literature uses these molecules as cross-coupling substrates, ring-construction intermediates, and tracer precursors.

4.2 Radiolabeled Iodinated Heterocyclic Compounds

Structurally, these molecules still belong to iodinated heterocycles, but they are more specialized in terms of use because the iodine involved is often a radioactive isotope such as ¹²³I, ¹²⁵I, or ¹³¹I. They are used for SPECT imaging, therapeutic research, or pharmacokinetic tracing. Representative examples include the radioiodinated 2-nitroimidazole probe IAZA for hypoxia-related studies, iodinated heterocyclic probes such as IMPY for β-amyloid imaging, and molecules such as MNI-187 that remain at the research or clinical evaluation stage.

4.3 Cyclic Hypervalent Iodine Heterocyclic Systems

These systems are no longer simply “heterocycles bearing an ordinary iodine substituent.” Instead, iodine itself is in a hypervalent state and is stabilized as part of a ring system. The most typical examples are benziodoxol(on)e, benziodazol(on)e, and their derivatives. They commonly function as I(III) or I(V) reagents for oxidation, alkynyl transfer, trifluoromethyl transfer, aryl transfer, and a variety of oxidative functionalization processes. Because cyclization can improve stability and modulate reactivity, this class of molecules is highly important in modern methodology.

4.4 Classification of Iodine-Containing Heterocyclic Organic Compounds

Category	Key structural feature	Common research role
Ordinary iodinated heterocycles	Covalent C–I bond on a heterocyclic scaffold	Substrates, synthetic intermediates, radiolabeling precursors
Radiolabeled iodinated heterocycles	Radioiodine isotopes introduced into a heterocyclic scaffold	Imaging probes, therapy-oriented research molecules, pharmacokinetic tracers
Cyclic hypervalent iodine heterocycles	Iodine is in a high oxidation state such as I(III)/I(V) and is stabilized by a ring system	Oxidants, group-transfer reagents, catalytic platforms

V. Application Areas and Unique Roles

5.1 Organic Synthesis and Heterocycle Construction

This is the most central and most widespread application scenario. Ordinary iodinated heterocycles are frequently used as cross-coupling substrates, regioselective post-functionalization intermediates, or relay points in multistep synthetic routes. At the same time, iodine-promoted cyclization reactions can directly generate new iodinated heterocycles, thereby accomplishing both “ring construction” and “reservation of a downstream functionalization handle” in a single operation. Reviews of molecular iodine-promoted cyclization clearly show that iodine can promote cyclization of O-, N-, and S-containing alkenyl/alkynyl substrates to form a wide range of heterocycles, including furans, pyrroles, thiophenes, indoles, benzofurans, and benzothiophenes.

5.2 Assembly of Polyheterocyclic Scaffolds

In some studies, iodine is not retained to the final step; instead, iodinated heterocycles are used as “iteratively extendable relay stations.” Representative work based on tandem iodine/palladium strategies shows that researchers can first construct alkynyl intermediates via Sonogashira coupling, then obtain 3-iodoheterocycles through iodocyclization, and subsequently continue with further coupling and cyclization to build up polyheterocyclic molecules step by step. This approach is particularly suitable for route design that requires the sequential assembly of multiple heterocyclic modules.

5.3 Radiotracer Imaging and Therapeutic Research

Radioiodine is widely used in nuclear medicine, while heterocycles often provide better target recognition or pharmacologically relevant scaffolds. Their combination has therefore produced a number of important tracer and therapy-oriented research molecules. Examples mentioned above include the hypoxia-related radioiodinated probe IAZA and β-amyloid imaging probes such as IMPY. In this field, iodine is not merely a substituent, but a signal source capable of reporting in vivo distribution information.

5.4 Halogen-Bond Catalysis, Molecular Recognition, and Supramolecular Assembly

IUPAC defines halogen bonding as the net stabilizing interaction formed between a Lewis acidic halogen atom and a Lewis basic region. Because iodine is highly polarizable, it is often a relatively strong halogen-bond donor. In recent years, N-heterocyclic iod(az)olium salts have been shown to act as highly active halogen-bonding organocatalysts and can activate substrates such as halides, carbonyl compounds, and nitro compounds. Related studies also indicate that halogen bonding has broad applications in crystal engineering, functional materials, and molecular recognition.

5.5 Hypervalent Iodine Methodology and Greener Alternatives

Hypervalent iodine chemistry is one of the fastest-growing branches of organoiodine research. Reviews indicate that I(III) and I(V) reagents can serve as mild and relatively selective tools for oxidation and functionalization, and in many scenarios they are regarded as alternatives to heavy-metal reagents. In particular, cyclic hypervalent iodine platforms such as benziodoxolone, benziodazolone, EBX, and Togni-reagent-related systems are highly active in oxidation, C–N / C–O / C–C bond construction, and group-transfer reactions.

5.6. Major Application Areas and Representative Roles

Application area	More common molecular type	Unique role
Heterocycle synthesis and post-functionalization	Ordinary iodinated heterocycles	Serve as highly reactive handles for coupling, substitution, and radical transformation
Assembly of polyheterocyclic scaffolds	Ordinary iodinated heterocycles	Act as iteratively extendable intermediates for continuous construction of multi-ring systems
Nuclear-medicine imaging / therapy-oriented research	Radiolabeled iodinated heterocycles	Provide tracer signals together with structurally recognizable scaffolds
Halogen-bond catalysis and molecular recognition	Iodine-containing heterocycles, hypervalent iodine heterocycles	Provide relatively directional noncovalent interactions
Oxidation and group-transfer methodology	Hypervalent iodine heterocycles	Function as mild reagents or catalytic platforms to drive reactions

VI. When to Consider Choosing Iodine-Containing Heterocyclic Organic Compounds

6.1 When a Heterocyclic Site That Is Easy to Modify Later Is Needed

If the goal is to first construct a heterocyclic scaffold and then introduce aryl, alkenyl, alkynyl, amino, or other fragments at a specific position, an iodinated heterocycle is often more suitable than an unactivated heterocycle. In this context, iodine is not the end point, but a high-value synthetic handle.

6.2 When Ring Construction and Handle Installation Are Intended to Be Combined into One Step

For O/N/S-containing enyne or enone-type precursors, iodine-promoted cyclization can often directly deliver new iodinated heterocycles. If coupling or derivatization is needed afterward, this route is usually more direct than first building the ring and then carrying out site-selective functionalization.

6.3 When the Research Involves SPECT, Therapeutic Tracing, or Precursors for Radiopharmaceuticals

In such cases, priority should be given to heterocyclic scaffolds that can both stably carry radioiodine and retain the desired recognition ability. For these projects, structural selection cannot be based only on “whether iodine can be introduced”; it must also take into account “whether deiodination will occur in vivo” and “whether labeling alters pharmacological activity or biodistribution.”

6.4 When Mild Oxidation, Group Transfer, or Metal-Replacement-Type Methodology Is Needed

If the goal is not to retain iodine in the final product but to use iodine to drive oxidation, alkynyl transfer, aryl transfer, or nonmetal catalysis, then hypervalent iodine heterocyclic platforms should be prioritized rather than ordinary iodinated heterocycles.

VII. Points to Note When Selecting or Using These Compounds

7.1 First Distinguish Whether You Need a “Substrate” or a “Reagent”

This is the point most likely to cause confusion and also the one that should be clarified first. Ordinary iodinated heterocycles are mainly the objects being transformed, whereas hypervalent iodine heterocycles are mainly tools that drive transformations. If these two are mixed up, the subsequent route design, stoichiometry, condition screening, and safety evaluation may all become misleading.

7.2 Heteroatoms May Make Coupling More Difficult

Although the C–I bond is often an excellent transformation site, that does not mean every iodinated heterocycle is “naturally easy to couple.” Some electron-rich five-membered heterocycles may compete for coordination with Pd and other metal centers, leading to catalyst deactivation or slower key steps; some substrates are also sensitive to strong bases. In other words, iodinated heterocycles often require more careful condition optimization and cannot simply be treated in the same way as iodobenzene.

7.3 In Radiolabeling Projects, Special Attention Should Be Paid to In Vivo Deiodination

Radiopharmaceutical design involving radioiodine requires particular attention to the risk of in vivo deiodination. As a general trend, radioiodine attached to an sp² carbon of an iodoarene or to an iodovinyl fragment is often relatively more stable, whereas many iodinated heterocycles are more prone to in vivo deiodination. However, the actual stability still depends on the type of heterocycle, the substitution pattern, and the overall electronic environment, so evaluation should be carried out on a case-by-case basis for the target scaffold.

7.4 Although Hypervalent Iodine Systems Are Often Mild, Safety and Compatibility Still Need to Be Evaluated

Hypervalent iodine chemistry is often described as mild, selective, and capable of replacing some heavy-metal systems, and this overall assessment is valid. However, in practical experiments, such reagents are still highly reactive species. Their thermal stability, sensitivity to water and nucleophiles, and scale-up risks may vary from system to system, so “mild” should not be taken to mean “no additional evaluation needed.”

7.5 Decide in Advance Whether the Iodine Is Intended to Remain in the Final Product

In some projects, the final product is expected to retain iodine in order to take advantage of halogen bonding, imaging properties, or electronic effects; in others, iodine serves only as a temporary handle and will eventually be replaced during coupling or post-functionalization. These two strategies lead to different selection criteria: the former focuses more on final properties and stability, whereas the latter focuses more on reaction compatibility, regioselectivity, and route efficiency.

VIII. Product Navigation for Iodine-Containing Heterocyclic Organic Compounds: Quickly Locate Tables 1–4 by Research Task

Research task / experimental need	Product types to prioritize	Recommended table to consult first	Navigation notes
DNA replication, cell proliferation, nucleic acid incorporation, or DNA synthesis tracing experiments	Iodinated deoxynucleosides such as 5-Iodo-2′-deoxyuridine and 5-Iodo-2′-deoxycytidine	Table 1	Table 1 focuses on nucleosides, nucleobases, and purine/pyrimidine precursors. Halogenated nucleosides are especially suitable for DNA/RNA-related experiments, replication tracing, and nucleic acid modification studies.
RNA modification, nucleoside analogs, nucleobase analogs, or nucleic acid probe development	Iodouridine, iodoadenosine, iodouracil, iodocytosine, etc.	Table 1	If the research focus is nucleic acid chemistry, nucleoside medicinal chemistry, enzyme recognition, or site-specific modification, Table 1 is the most direct choice because the products themselves are built on nucleic-acid-related scaffolds.
Derivatization at purine / pyrimidine positions, or expansion of nucleic-acid-related structural diversity through coupling	2-Iodopyrimidine, 5-Iodopyrimidine, 6-Iodopurine, 7-deaza-iodoadenosine, etc.	Table 1	Table 1 is suitable not only for biochemical studies, but also for use as medicinal-chemistry precursors, especially for SAR expansion starting from nucleobase or nucleoside scaffolds.
Suzuki, Sonogashira, Buchwald–Hartwig, and related couplings of six-membered nitrogen heteroarenes such as pyridines, pyrazines, quinolines, and isoquinolines	2-/3-/4-Iodopyridine, 2-Iodopyrazine, 3-Iodoquinoline, 4-Iodoisoquinoline	Table 2	Table 2 corresponds to one of the most commonly used classes of iodinated N-heteroaromatic building blocks in medicinal chemistry, making it suitable for site-selective substitution and rapid expansion of lead structures.
Lead optimization centered on nitrogen-containing fused heterocycles	Iodoindoles, iodoazaindoles, iodoindazoles, iodobenzimidazoles	Table 2	In addition to six-membered N-heteroarenes, Table 2 also includes high-frequency fused nitrogen heterocycles used in medicinal chemistry, making it suitable for local modification and structure–activity relationship studies around active scaffolds.
Extension of heterocyclic fragments in lead compounds such as kinase inhibitors, receptor ligands, and enzyme inhibitors	3-Iodo-7-azaindole, 5-Iodoindazole, 4-Iodobenzimidazole, 3-Iodoquinoline, etc.	Table 2	If the goal is not simply to obtain “heterocyclic raw materials” but to optimize structure directly around typical pharmacophore-containing scaffolds, Table 2 is usually more practical.
Synthesis of derivatives of five-membered heteroarenes such as pyrazoles, imidazoles, thiazoles, thiophenes, and furans	4-Iodopyrazole, 4-/5-Iodothiazole, 4-Iodoimidazole, 2-Iodofuran, etc.	Table 3	Table 3 covers non-fused five-membered heteroaromatic iodinated building blocks and is suitable for basic heterocycle coupling, medicinal-chemistry intermediate synthesis, and methodology screening.
Conjugated thiophene / furan monomers, functional-material monomers, or double-coupling expansion	2-Iodothiophene, 3-Iodothiophene, 2,5-Diiodothiophene, 2-Iodofuran	Table 3	If the work leans toward organic electronic materials, extension of conjugated systems, or two-site coupling, Table 3 is more appropriate, especially for bifunctional monomers such as 2,5-Diiodothiophene.
Comparison of the effects of different iodination positions within the same five-membered heterocycle on reactivity or SAR	2-/3-Iodothiophene, 4-/5-Iodothiazole, 4-Iodoimidazole and its N-methylated derivative	Table 3	Table 3 is suitable for positional-isomer comparisons, reaction-condition exploration, and small-scale SAR studies. Readers can search directly by heterocycle type and iodination position.
Modern synthetic methodology such as trifluoromethylation, alkynylation, and oxidative group transfer	Togni reagents, EBX reagents, benziodoxolone-type hypervalent iodine(III) reagents	Table 4	The first half of Table 4 is not a section of ordinary iodinated heterocyclic building blocks, but a dedicated area for hypervalent iodine reagents. If the goal is efficient introduction of CF₃, alkynyl groups, or oxidative transformations, Table 4 should be consulted first.
Radical reactions, late-stage functionalization, electrophilic alkynyl transfer, or electrophilic trifluoromethylation	EBX-type alkynyl-transfer reagents, Togni-type CF₃-transfer reagents	Table 4	These experiments focus more on reagent function than on the heterocyclic scaffold itself, so the most suitable hypervalent iodine reagents should be selected directly from Table 4.
SPECT neuroimaging, DAT imaging, D2/D3 receptor imaging, or radiopharmaceutical-related research	Radiolabeled neuroimaging ligands such as Altropane I-123, IBZM, and ioflupane	Table 4	The second half of Table 4 collects radioiodinated neuroimaging-related products and is suitable for neurodegenerative disease research, receptor-occupancy studies, and radiotracer development.
Quick table selection along two main lines: “biology-related” and “synthetic-methodology-related”	Biology-related: nucleic acid chemistry, pharmacophore scaffolds, neuroimaging; methodology-related: coupling building blocks, hypervalent iodine reagents	For biology-related topics, start with Tables 1, 2, and 4; for synthetic construction, start with Tables 2, 3, and 4	If the goal involves nucleic acids, bioactive molecules, or neuroimaging, it is most efficient to begin with Tables 1, 2, and 4. If the goal is heterocycle construction, cross-coupling, or group-transfer chemistry, it is more efficient to begin with Tables 2, 3, and 4.

Table 1 | Iodine-Containing Heterocycles Relevant to Nucleic Acid Chemistry: Nucleosides, Nucleobases, and Purine/Pyrimidine Precursors

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
Iodinated deoxynucleosides (pyrimidine type)	54-42-2	I101755	5-Iodo-2′-deoxyuridine	≥99%	A classic halogenated deoxynucleoside; can be incorporated into newly synthesized DNA and is widely used in cell proliferation/replication tracing, DNA synthesis studies, antibody detection systems, and radiosensitization-related research; its C5–I position also facilitates further functionalization.
Iodinated deoxynucleosides (pyrimidine type)	611-53-0	I119526	5-Iodo-2′-deoxycytidine	≥99%	A halogenated deoxycytidine analog commonly used in DNA chemical modification, nucleoside medicinal chemistry, and enzyme-substrate studies; the C5–I position is suitable for introduction of aryl, alkynyl, and other substituents through coupling reactions.
Iodinated purine nucleoside analogs	166247-63-8	D649745	7-Deaza-2'-deoxy-7-iodoadenosine	≥99%	A 7-deazaadenosine-type nucleoside modification building block; widely used in nucleic acid probes, nucleoside analogs, and receptor/enzyme ligand development; the iodine at the 7-position is an efficient cross-coupling site.
Iodinated ribonucleosides (pyrimidine type)	1024-99-3	I119472	5-Iodouridine	≥97%(HPLC)	An iodinated uridine derivative widely used in RNA/nucleoside chemical modification, enzyme recognition studies, and C5-position cross-coupling derivatization; it is an important intermediate for the synthesis of nucleic acid probes and nucleoside analogs.
Iodinated purine nucleoside analogs	35109-88-7	I135473	2-Iodoadenosine	≥97%	An adenosine analog that can be modified at the C2 position; used in adenosine receptor ligand research, nucleoside probes, and nucleoside medicinal chemistry, and also suitable for subsequent coupling to expand structural diversity.
Iodinated pyrimidine bases	696-07-1	I124244	5-Iodouracil	≥99%	An iodinated pyrimidine-base precursor used in studies of halogenated nucleobases, nucleoside synthesis precursors, and derivatization at the C5 position of the pyrimidine ring; a common basic building block in nucleic acid chemistry and medicinal chemistry.
Iodinated pyrimidine bases	1122-44-7	I137433	5-Iodocytosine	≥98%	An iodinated cytosine base used as a nucleobase analog, a nucleoside synthesis precursor, and a substrate for further C5 functionalization; representative in nucleic acid modification and medicinal-chemistry screening.
Iodinated pyrimidine heterocyclic building blocks	31462-58-5	I192676	5-Iodopyrimidine	≥98%	A commonly used iodinated intermediate for pyrimidine-based pharmacophore scaffolds; suitable for constructing 5-substituted pyrimidine derivatives and frequently used in medicinal chemistry, nucleic acid chemistry, and heterocyclic methodology research.
Iodinated pyrimidine heterocyclic building blocks	31462-54-1	I404595	2-Iodopyrimidine	≥97%	An activated 2-iodopyrimidine building block suitable for constructing 2-substituted pyrimidine pharmacophore scaffolds; commonly used in lead optimization and diversity-oriented coupling reactions in medicinal chemistry.
Iodinated purine bases	2545-26-8	I169066	6-iodopurine	≥95%	An activated purine precursor at the 6-position; commonly used to prepare 6-substituted purines, nucleoside analogs, and kinase/receptor-related lead compounds; a classic intermediate in purine chemistry.

Table 2 | Iodinated Nitrogen-Containing Heteroaromatic Building Blocks Commonly Used in Medicinal Chemistry: Six-Membered Rings and Fused Rings

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
Iodinated pyridine building blocks	5029-67-4	I111393	2-Iodopyridine	≥97%, with copper stabilizer	2-Iodopyridine is a commonly used heteroaryl coupling substrate; suitable for Suzuki, Sonogashira, Buchwald–Hartwig, and related reactions; used to construct 2-substituted pyridine scaffolds in medicinal chemistry and ligand chemistry.
Iodinated pyridine building blocks	1120-90-7	I101566	3-Iodopyridine	≥98%	A 3-iodopyridine intermediate suitable for site-selective construction of 3-substituted pyridine structures; widely used in drug leads, polynitrogen ligands, and functional molecule synthesis.
Iodinated pyridine building blocks	15854-87-2	I100877	4-Iodopyridine	≥98%	A high-frequency building block in heterocycle synthesis; commonly used for introduction of aryl, alkynyl, amino, and other functional groups, and suitable for medicinal chemistry and methodology development.
Iodinated pyrazine building blocks	32111-21-0	I157423	2-Iodopyrazine,Iodopyrazine	≥97%(GC)	An electron-deficient N-heteroaromatic iodinated building block suitable for cross-coupling to construct 2-substituted pyrazines; commonly encountered in anti-infective research, kinase inhibitors, and exploration of electron-accepting scaffolds.
Iodinated quinoline building blocks	79476-07-6	I725773	3-Iodoquinoline	≥95%	An iodinated intermediate of a fused N-heteroaromatic scaffold; suitable for site-diverse modification of quinoline frameworks and commonly used in medicinal chemistry, fluorescent probes, and heterocyclic methodology research.
Iodinated isoquinoline building blocks	55270-33-2	I185172	4-Iodoisoquinoline	≥95%	A commonly used iodinated isoquinoline pharmacophore scaffold; used to construct 4-substituted isoquinoline derivatives and suitable for medicinal-chemistry lead optimization and coupling methodology.
Iodinated indole building blocks	26340-47-6	I725702	3-Iodoindole	≥98%	An iodinated intermediate at the C3 position of indole; suitable for constructing 3-substituted indoles and widely used in natural-product analogs, medicinal chemistry, and heterocycle coupling methodology.
Iodinated indole building blocks	16066-91-4	I122983	5-Iodoindole	≥98%	An iodinated indole at the benzene-ring position; suitable for coupling-based modification at C5 and commonly used to construct receptor ligands, fluorescent probes, and bioactive molecules.
Iodinated azaindole building blocks	23616-57-1	I122921	3-Iodo-7-azaindole	≥97%	7-Azaindole is a classic hinge-binding scaffold for kinase inhibitors; this product is suitable for site-specific coupling at C3 and is used in kinase medicinal chemistry and fragment expansion.
Iodinated indazole building blocks	55919-82-9	I176793	5-iodo-1H-indazole	≥97%	A commonly used iodinated intermediate of an indazole pharmacophore scaffold; facilitates introduction of diverse substituents at the aromatic-ring position and is widely used in lead optimization of kinase, receptor, and enzyme inhibitors.
Iodinated benzimidazole building blocks	51288-04-1	I1071657	4-Iodo-1H-benzimidazole	≥95%	A precursor for benzimidazole heterocycle modification; suitable for diversified modification of fused heterocycles in anti-infective, antitumor, and ligand chemistry research.

Table 3 | Iodinated Five-Membered Heteroaromatic Building Blocks: Sulfur-, Nitrogen-, and Oxygen-Containing Heterocycles

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
Iodinated pyrazole building blocks	3469-69-0	I157632	4-Iodopyrazole	≥98%(HPLC)	A key-site iodinated intermediate for pyrazole pharmacophore scaffolds; suitable for rapid construction of polysubstituted pyrazoles by cross-coupling and commonly used in medicinal chemistry and agrochemical lead synthesis.
Iodinated thiophene building blocks	3437-95-4	I107041	2-Iodothiophene	≥97%, with copper stabilizer	A classic thiophene coupling monomer suitable for preparing substituted thiophenes, conjugated oligomers, and medicinal-chemistry heterocyclic fragments; it can also be used in metal-catalyzed coupling and organic electronic material synthesis.
Diiodothiophene bis-coupling building blocks	625-88-7	D155849	2,5-Diiodothiophene	≥97%(GC)	A bifunctional monomer containing two coupling sites; suitable for constructing symmetric thiophene derivatives, conjugated polymers, OLED/OFET/OPV materials, and multistep tandem syntheses.
Iodinated thiophene building blocks	10486-61-0	I165643	3-Iodothiophene	≥97%	A 3-iodothiophene intermediate commonly used to prepare 3-substituted thiophenes, functional-material monomers, and medicinal-chemistry fragments; suitable for cross-coupling and organometallic transformations.
Iodinated thiazole building blocks	108306-60-1	I1008042	4-Iodo-1,3-thiazole	≥97%	An iodinated key-site intermediate of a thiazole pharmacophore scaffold; suitable for site-specific coupling at the 4-position and commonly used in drug, agrochemical, and sulfur-containing heterocycle methodology development.
Iodinated thiazole building blocks	108306-61-2	I1054333	5-Iodo-1,3-thiazole	≥95%	A 5-iodothiazole intermediate that helps support positional-isomer comparison and SAR optimization; commonly used for site-specific modification of pharmaceutical and agrochemical leads.
Iodinated imidazole building blocks	71759-87-0	I177269	4-iodo-1-methyl-1H-imidazole	≥97%	A C4-iodinated precursor of N-methylimidazole; convenient for constructing substituted imidazole derivatives and suitable for medicinal chemistry, coordination ligands, and functional molecule synthesis.
Iodinated imidazole building blocks	71759-89-2	I115819	4-Iodo-1H-imidazole	≥97%	A precursor for C4 functionalization of the imidazole ring; used to construct imidazole derivatives with hydrogen-bond-recognition and coordination ability, and commonly seen in medicinal chemistry and catalytic ligand research.
Iodinated furan building blocks	54829-48-0	I726108	2-IODOFURAN (STABILIZED WITH COPPER CHIP)	≥95%	A basic furan cross-coupling building block suitable for constructing 2-substituted furans, natural-product analogs, and oxygen-containing heterocyclic fragments; it can also be used in materials and fragrance-related synthesis research.

Table 4 | Hypervalent Iodine(III) Reagents and Radiolabeled Iodine Products Related to Neuroimaging

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
Benziodoxolone core parent / precursor	131-62-4	H586982	1-Hydroxy-1,2-benziodoxol-3(1H)-one	≥97%	The core parent structure of benziodoxolone; can serve as a synthetic precursor for a variety of EBX- and Togni-type hypervalent iodine reagents, and is also used in hypervalent iodine platform chemistry and oxidation research.
Benziodoxolone oxidation / transfer reagent	1829-26-1	A709522	1-Acetoxy-1,2-benziodoxol-3-(1H)-one	≥97%	A hypervalent iodine(III) platform reagent commonly used in oxidative group-transfer reactions, acyloxylation, and related methodology development; also an important precursor for constructing more complex benziodoxolone reagents.
EBX alkynyl-transfer reagent	181934-30-5	T465298	1-[(Triisopropylsilyl)ethynyl]-1,2-benziodoxol-3(1H)-one	≥98%(AT)	A classic EBX-type hypervalent iodine alkynyl-transfer reagent; commonly used in electrophilic alkynylation, radical alkynylation, and C–H functionalization, and highly representative in alkynyl-introduction methodology.
EBX alkynyl-transfer reagent / precursor	181934-29-2	T161694	1-[(Trimethylsilyl)ethynyl]-1,2-benziodoxol-3(1H)-one	≥95%	A TMS-protected EBX-type alkynyl iodine(III) reagent used for electrophilic alkynylation; it can also serve as an intermediate for the further preparation of other alkynyl benziodoxolone reagents.
Togni-type trifluoromethylation reagent	887144-97-0	T162595	1-Trifluoromethyl-3,3-dimethyl-1,2-benziodoxole	≥97%(HPLC)	A Togni-type CF₃-transfer reagent used in electrophilic or radical trifluoromethylation; suitable for late-stage introduction of trifluoromethyl groups in medicinal chemistry to tune lipophilicity, metabolic stability, and activity.
Togni-type trifluoromethylation reagent	887144-94-7	T189226	1-Trifluoromethyl-1,2-benziodoxol-3-(1H)-one	≥97%	Another commonly used Togni-type hypervalent iodine CF₃ reagent; suitable for trifluoromethylation studies of alkenes, heteroarenes, nucleophilic substrates, and radical systems.
Radiolabeled dopamine transporter (DAT) imaging ligand / tropane-based neuroimaging probe	208517-65-1	A671277	Altropane I-123	——	An iodine-123-labeled tropane-based DAT imaging probe used for studies of dopamine transporter imaging in the brain; commonly applied to evaluation of neurodegenerative changes associated with parkinsonian syndromes, mapping of striatal DAT distribution, and SPECT radiopharmaceutical development.
Radiolabeled dopamine D2/D3 receptor imaging ligand	84226-06-2	I333289	IBZM	——	An iodinated benzamide neuroreceptor imaging ligand commonly used for dopamine D2/D3 receptor imaging and receptor-occupancy studies; suitable for neuropsychopharmacology, receptor-binding evaluation, and SPECT-related radiotracer research.
Radiolabeled dopamine transporter (DAT) imaging ligand / tropane-based neuroimaging probe	155798-07-5	I611126	ioflupane	Moligand™	A tropane-based DAT imaging ligand and a representative molecule in neuroimaging and radiopharmaceutical research; commonly used for visualization of striatal dopamine transporters, Parkinson’s disease-related research, tracer development, and establishment of SPECT imaging methods.

Note: The products listed above are representative Aladdin products. For additional specifications, please refer to the product list at the end of the article or search the Aladdin website using the product name / CAS / catalog number.

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