Experimental Assessment of Dibenzyl N,N-Diisopropylphosphoramidite for Alcohol O-Phosphorylation: Coupling, Oxidation, and Debenzylation

Introduction | The Basic Framework of the Dibenzyl N,N-Diisopropylphosphoramidite Route

In alcohol O-phosphorylation, dibenzyl N,N-diisopropylphosphoramidite does not correspond to a one-step construction of the free phosphate. Rather, it belongs to a stepwise synthetic route. In the initial stage, a protected phosphate fragment is first attached to the alcohol in the form of a trivalent phosphorus species; in the middle stage, the intermediate is oxidized to a pentavalent phosphorus product; and in the final stage, the two benzyl groups are removed to release the target phosphate. The 1988 work of Yu and Fraser-Reid on the synthesis of inositol phosphates already illustrated the basic framework of this route. Perich and Johns in 1987 more directly demonstrated the use of dibenzyl phosphoramidite reagents for O-phosphorylation of alcohol substrates, followed by oxidation to furnish benzyl-protected phosphate triesters. The review by Beaucage and Iyer in 1993 further showed that the phosphoramidite method is not limited to oligonucleotide assembly, but is also applicable to the construction of other phosphorylated biomolecules.

Experimentally, this route usually requires sequential evaluation of three questions: whether the initial-stage installation proceeds smoothly, whether the oxidation step is clean, and whether the final debenzylation is compatible with both the substrate and the overall protecting-group design. The first stage determines whether the protected phosphate fragment can be effectively installed onto the target alcohol site; the middle stage determines whether the trivalent phosphorus intermediate can be reliably converted into the pentavalent phosphorus product; and the final stage determines whether the protected phosphate intermediate obtained earlier can ultimately be transformed into the target free phosphate. In this type of route, the initial bond-forming step, the post-coupling oxidation, and the final debenzylation are not independent operations, but three connected decision points. Even when the initial coupling is feasible, the overall route may still be limited by oxidation-sensitive functionality in the substrate, or by incompatibility between the final debenzylation conditions and the overall protecting-group strategy.

1. First Obtain a Protected Phosphate Intermediate, Then Release the Free Phosphate

The product formed in the initial stage of the dibenzyl N,N-diisopropylphosphoramidite route is typically a benzyl-protected phosphate intermediate rather than the final free phosphate monoester. Such intermediates are easier to isolate, store, and carry forward into subsequent transformations, and they are also easier to incorporate into a unified protecting-group plan for the entire synthetic sequence. The work of Yu and Fraser-Reid followed exactly this logic: a benzyl-protected phosphate product was first obtained, and the free phosphate was then released through subsequent debenzylation.

1.1 Three Key Stages of the Dibenzyl N,N-Diisopropylphosphoramidite Route

Step	Questions That Need to Be Evaluated	Possible Problems
Initial-stage installation	Is the alcohol site sufficiently reactive? Is the activator appropriate? Is the system sufficiently anhydrous?	Incomplete coupling, residual starting material, insufficient conversion in the initial stage
Oxidation step	Can the trivalent phosphorus intermediate be smoothly converted into the pentavalent phosphorus product? Can the substrate tolerate the oxidation conditions?	Mixed phosphorus valence states, increased side reactions, heavier purification burden
Debenzylation	Can the benzyl groups be removed smoothly within the current molecular framework? Will other sensitive sites be affected?	The protected intermediate is obtained, but the target free phosphate is difficult to release in the final stage

2. Activator Selection and Substrate Compatibility in the Initial Coupling Step

Whether the initial coupling proceeds smoothly is closely related to activator selection. The study by Berner et al. in 1989 showed that tetrazole, when involved in phosphoramidite activation, can form tetrazole-related activated intermediates while also serving as a proton donor. Differences in the initial coupling step are reflected not only in reaction rate, but also in the activation process itself and in the balance of the reaction system.

4,5-Dicyanoimidazole was developed on the basis of this class of activation studies. In 1998, Vargeese et al. reported in a nucleoside phosphoramidite coupling system that the solubility of 4,5-dicyanoimidazole in acetonitrile could reach 1.1 mol/L, and that the coupling time was about half that required for the 1H-tetrazole system. For certain sterically hindered nucleoside phosphoramidite substrates, the coupling time could be shortened from 25 minutes to 10 minutes. The study attributed this performance to the higher nucleophilicity of 4,5-dicyanoimidazole, together with the higher effective activation concentration made possible by its higher solubility.

These results indicate that, when the initial coupling involves phosphoramidite systems that are sterically hindered, intrinsically slow-reacting, or require a higher effective activation concentration, the choice of activator can significantly affect coupling efficiency. Existing reports are concentrated mainly on nucleoside phosphoramidite and oligonucleotide-related coupling systems. When applied to dibenzyl N,N-diisopropylphosphoramidite, these results can serve as references for initial-stage activator selection and for difficult coupling situations, but the actual outcome still needs to be verified on the specific substrate. Because direct comparisons between 1H-tetrazole and DCI mainly come from nucleoside phosphoramidite and oligonucleotide coupling systems, it is more appropriate to regard them as references for activation trends when dealing with general alcohol substrates, rather than directly extrapolating them as universal conclusions.

2.1 Comparison of 1H-Tetrazole and DCI in the Initial Coupling Step

Comparison Item	1H-Tetrazole	4,5-Dicyanoimidazole (DCI)	Key Point for Evaluation
Methodological role	Classical activator	Common alternative activator	Both are used in the initial coupling step
Activation characteristics	Forms tetrazole-related activated intermediates and also acts as a proton donor	Higher nucleophilicity and higher solubility in acetonitrile	Focus on coupling rate and substrate compatibility
Reported performance	Mature method with a long history of use	Faster in some difficult phosphoramidite coupling systems	Worth prioritizing for comparison when steric hindrance is high or the reaction is slow
Scope of application	Related studies are mainly found in nucleoside phosphoramidite and oligonucleotide coupling systems	Related studies are mainly found in nucleoside phosphoramidite and oligonucleotide coupling systems	Still requires experimental validation on the specific substrate

3. Compatibility of the Oxidation Step and Control of Product Formation

The initial coupling step generates a trivalent phosphorus intermediate, which must then undergo oxidation before reaching the more stable pentavalent phosphorus product stage. In the 1988 work of Yu and Fraser-Reid on inositol phosphate synthesis, this transformation was accomplished with mCPBA. More recent methodological reviews generally describe the phosphoramidite route as involving initial installation of a trivalent phosphorus intermediate, oxidation to a pentavalent phosphorus product, and final deprotection.

Experimentally, the oxidation step mainly needs to be evaluated from three aspects.

1. Whether the substrate contains functional groups that are sensitive to oxidation conditions. This determines whether the oxidation step can proceed smoothly within the current molecular framework.

2. Whether the trivalent phosphorus intermediate can be cleanly converted into the pentavalent phosphorus product. If this step is poorly controlled, incomplete oxidation and more complicated product mixtures can arise, making subsequent characterization and purification more difficult.

3. Whether the oxidized protected phosphate intermediate is suitable for subsequent debenzylation or for the next transformation. This affects whether the entire route can proceed smoothly from one stage to the next.

3.1 Key Points for Evaluating the Oxidation Step

Evaluation Item	What Needs to Be Examined	Impact on the Experiment
Compatibility of oxidation conditions	Whether the substrate contains oxidation-sensitive sites	Affects whether this step can be completed smoothly
Product conversion	Whether the trivalent phosphorus intermediate can be cleanly converted into the pentavalent phosphorus product	Affects subsequent characterization and purification
Connection to downstream steps	Whether the oxidized intermediate is suitable for subsequent debenzylation or the next transformation	Affects the continuity and efficiency of the entire route

4. Debenzylation and Overall Protecting-Group Design

In the later stage of the dibenzyl N,N-diisopropylphosphoramidite route, the free phosphate still has to be released through debenzylation. The 1988 work of Yu and Fraser-Reid already reflected this feature: a benzyl-protected phosphate product was first obtained in the initial stage, and the target phosphate was then generated through subsequent debenzylation. For routes that require isolation of protected phosphate intermediates, or that plan to remove multiple benzyl protecting groups together in the later stage, this arrangement is relatively easy to integrate into the overall synthetic sequence.

Whether debenzylation is feasible depends on the substrate’s tolerance to the conditions used in the later stage. If the molecule contains hydrogenolysis-sensitive or reduction-sensitive sites that must be retained, the debenzylation step may become the limiting factor for the entire route. The triethylsilane-mediated debenzylation method reported by Hodson et al. in 2025 expanded the range of condition choices for phosphate debenzylation and showed applicability to redox-sensitive functional groups. Even so, whether a specific substrate can be smoothly debenzylated still needs to be verified experimentally in the actual system.

The type of target product also affects the priority of this route. If the research task requires a protected phosphate intermediate first, followed by subsequent transformations, the dibenzyl-protected route is easier to organize. If the goal is to obtain the free phosphate monoester as quickly as possible, however, the stepwise sequence of protection, oxidation, and deprotection may not offer an advantage in step economy, and it will usually need to be compared alongside direct alcohol O-phosphorylation methods.

4.1 Suitability Assessment of the Dibenzyl-Protected Route in the Final Debenzylation Stage

Situation	Implication for the Route	Suggested Assessment
Isolation and storage of a protected phosphate intermediate are required	The protected intermediate facilitates subsequent operations and stepwise progression	Can be prioritized
Multiple benzyl protecting groups are planned to be removed together in the later stage	The phosphate site can be integrated into the overall deprotection plan	Usually suitable
The molecule contains hydrogenolysis-sensitive or reduction-sensitive sites that must be retained	Debenzylation may become a limiting factor in the later stage	Compatibility should be tested as early as possible
Mild debenzylation conditions are acceptable for evaluation	The applicable scope of the route may be moderately broadened	Can be included in comparison
The goal is to obtain the free phosphate monoester as quickly as possible	The stepwise route does not have an obvious advantage in step economy	Not necessarily the first choice

5. Comparing the Dibenzyl-Protected Phosphoramidite Route with Direct Alcohol O-Phosphorylation Methods by Experimental Endpoint

The dibenzyl N,N-diisopropylphosphoramidite route should be compared not only with traditional protected phosphate strategies, but also with direct alcohol O-phosphorylation methods developed in recent years. Domon et al. in 2020 reported a catalytic and chemoselective direct alcohol O-phosphorylation method. Ociepa, Knouse, Baran, and co-workers in 2021 reported the Ψ reagent approach, which provides a direct, scalable, and chemoselective alcohol phosphorylation pathway based on preformed pentavalent phosphorus reagents. Both approaches aim to provide a more direct route to free phosphate monoesters, but the way the reactions are organized is not identical, so they should be evaluated separately in experimental comparisons.

Different experimental endpoints lead to different route priorities. When a protected phosphate intermediate is needed, the dibenzyl-protected route is easier to connect with subsequent transformations. When the goal is to obtain the free phosphate monoester as quickly as possible, direct alcohol O-phosphorylation methods are usually more worth prioritizing. These can in turn be further divided according to the task at hand into catalytic direct methods, methods based on preformed pentavalent phosphorus reagents, and other routes that lead directly to free phosphate monoesters.

Recent methodological advances continue to expand the scope of direct alcohol O-phosphorylation. The one-step electrochemical alcohol phosphorylation reported in 2025 further shows that direct methods are still expanding in both operational modes and substrate scope. However, such methods are not fully identical to catalytic direct methods or the Ψ reagent approach in terms of reaction organization and applicable substrate classes, and they should still be judged separately in comparison.

5.1 Choosing Between the Protected Route and Direct Phosphorylation Methods According to the Experimental Endpoint

Current Task	Route More Suitable for Priority Comparison	Main Reason
A protected phosphate intermediate is needed for subsequent transformation	Dibenzyl N,N-diisopropylphosphoramidite route	Facilitates stepwise organization and downstream connection
The goal is to obtain the free phosphate monoester as quickly as possible	Direct alcohol O-phosphorylation or direct pentavalent phosphorus phosphorylation methods	Can eliminate the debenzylation step
Phosphorylation of late-stage complex substrates, without wanting to introduce hydrogenolysis constraints	Compare direct methods first	Fewer limitations in the later stage
The molecule already contains multiple benzyl protecting groups, and unified removal is planned for the later stage	Dibenzyl-protected route	The phosphate site can be incorporated into the overall deprotection plan
The substrate contains sensitive sites, but a protected strategy is still preferred	Run parallel prescreening of both route types	Judgment still needs to be based on experimental results for the specific substrate

6. Product Navigation Table for the Use of Dibenzyl N,N-Diisopropylphosphoramidite in Alcohol O-Phosphorylation (Tables 1–3)

Research or Experimental Goal	Which Table to Consult	Why This Table	Which Table to Read in Combination	Navigation Note
To first distinguish the core reagent in this route, the upstream raw materials, and the protected phosphate intermediates	Table 1	Table 1 brings together dibenzyl N,N-diisopropylphosphoramidite, dibenzyl phosphite, phosphorus trichloride, diisopropylamine, benzyl alcohol, and dibenzyl phosphate, making it suitable for first establishing the overall framework of the route	Then read Table 3	First clarify what type of protected phosphate fragment is being introduced, and then judge whether the final-stage debenzylation is suitable for the current substrate
To judge whether the current alcohol substrate is suitable for the dibenzyl N,N-diisopropylphosphoramidite route	Table 1	Table 1 first answers fundamental questions such as the protecting-group plan, the source of the phosphorus-containing fragment, and the type of protected phosphate intermediate	Then read Tables 2 and 3	First determine whether a dibenzyl-protected phosphate intermediate is needed, and then move on to screening initial-stage activation and final-stage debenzylation
The route has been selected, and the initial coupling conditions need to be optimized	Table 2	Table 2 focuses on activators such as tetrazole, 4,5-dicyanoimidazole, 5-benzylthio-1H-tetrazole, and 5-ethylthio-1H-tetrazole, making it suitable for comparing initial bond-forming efficiency	Then read Table 1	The key to optimizing the initial coupling step lies in the activation system and substrate compatibility, not in final-stage deprotection
To screen post-oxidation conditions for conversion from trivalent phosphorus to pentavalent phosphorus	Table 2	Table 2 also includes post-oxidation components such as iodine, mCPBA, and tert-butyl hydroperoxide, making it convenient for comparing oxidation conditions	Then read Table 3	First clarify the post-oxidation conditions, and then proceed to final-stage debenzylation testing, making it easier to identify at which step the problem arises
The main concern is whether the two benzyl groups can be removed smoothly in the final stage, especially when the substrate contains reduction-sensitive sites	Table 3	Table 3 focuses on debenzylation-related components such as ammonium formate, palladium hydroxide, platinum oxide, and triethylsilane, making it suitable for prioritizing assessment of whether the final stage is limiting	Then read Table 1	If the room for final-stage debenzylation is limited, it is necessary to go back and reassess whether the dibenzyl-protected route is appropriate
To compare conventional hydrogenolytic debenzylation with milder debenzylation conditions	Table 3	Table 3 covers both palladium/platinum systems and triethylsilane, allowing comparison of substrate tolerance under different debenzylation conditions	Then read Table 2	Such comparisons should be made only after the initial coupling and post-oxidation steps are already under basic control
To compare the route of “trivalent phosphorus installation → oxidation → debenzylation” with routes that “directly deliver the free phosphate monoester”	Table 3	Phosphorus oxychloride in Table 3 can serve as a classical direct phosphorylation reference, allowing a preliminary comparison with the protected route of “trivalent phosphorus installation → oxidation → debenzylation”	Then read Table 1	If the goal is to obtain the free phosphate as quickly as possible, or if final-stage debenzylation is clearly limiting, the protected route should be compared first with different direct methods rather than using a single reference reagent as a substitute for all direct approaches
To conduct a systematic methodological study by separately comparing the route itself, the initial-stage conditions, and the final-stage deprotection	First read Table 1, then Table 2, and finally Table 3	The three tables correspond respectively to the route framework, initial-stage activation/post-oxidation, and final-stage debenzylation/reference routes, making stepwise study convenient	Read all three tables together	First fix the core installation reagent and protection strategy, and then separately compare activation, oxidation, and debenzylation conditions to obtain clearer conclusions

Table 1 | Core Trivalent Phosphorus Installation Reagent, Upstream Building Blocks, and Protected Phosphate Intermediates

Category	CAS No.	Aladdin Catalog No.	Name	Grade or Purity	Product Features and Applications
Upstream alcohol source for benzyl-protected fragments	100-51-6	B163018	Benzyl alcohol	Pharmaceutical grade, PharmPure™	Used to construct dibenzyl-protected phosphorus-containing intermediates such as dibenzyl phosphite and dibenzyl phosphate; suitable for routes in which the acidity of the phosphate is first masked with benzyl groups and final-stage debenzylation is then carried out.
Upstream amine source for phosphoramidite reagents	108-18-9	D108297	Diisopropylamine	Standard for GC, ≥99.5%(GC)	Used to introduce the diisopropylamino fragment and is a common upstream amine source for preparing trivalent phosphorus reagents such as dibenzyl N,N-diisopropylphosphoramidite; suitable for building reagent scaffolds that transfer the phosphoryl fragment under activation by tetrazole-type activators.
Upstream trivalent phosphorus precursor	7719-12-2	P475782	Phosphorus trichloride	Reagent grade, high purity, ≥99%	Commonly used to prepare phosphites, chlorophosphite intermediates, and phosphoramidite reagents; suitable for constructing the trivalent phosphorus framework at the upstream stage before moving on to dibenzyl-protected phosphorylation reagents.
Dibenzyl-protected phosphorus-containing precursor	17176-77-1	D135771	Dibenzyl Phosphite	≥95%	A commonly used dibenzyl-protected phosphorus-containing precursor that can be further converted into phosphoramidite reagents or other protected phosphorylation reagents; suitable for stepwise routes in which a protected phosphorus-containing fragment is obtained first, followed by coupling and post-oxidation.
Core trivalent phosphorus installation reagent	108549-23-1	D122720	Dibenzyl N,N-Diisopropylphosphoramidite	≥98%	Used to introduce a dibenzyl-protected phosphate fragment into alcohol substrates, usually in combination with activators such as tetrazole, 4,5-dicyanoimidazole, 5-benzylthio-1H-tetrazole, or 5-ethylthio-1H-tetrazole; suitable for first obtaining a protected phosphate intermediate and then completing subsequent transformations through oxidation and debenzylation.
Protected phosphate intermediate / reference compound	1623-08-1	D131779	Dibenzyl Phosphate	≥99%	Can serve as a reference compound for dibenzyl-protected phosphate products or related intermediates, helping determine whether post-oxidation has already reached the protected phosphate stage; suitable for establishing routes in which benzyl protection is retained first and removed later in a unified deprotection step.

Table 2 | Initial-Stage Coupling Activators and Post-Oxidation Components for Trivalent Phosphorus

Category	CAS No.	Aladdin Catalog No.	Name	Grade or Purity	Product Features and Applications
Classical tetrazole-type activator	288-94-8	T109596	Tetrazole	≥98%	One of the most commonly used activators in phosphoramidite coupling; suitable for establishing baseline conditions and evaluating the feasibility of bond formation between dibenzyl N,N-diisopropylphosphoramidite and alcohol substrates.
Highly efficient imidazole-type activator	1122-28-7	D109320	4,5-Dicyanoimidazole	≥99%	Commonly used to improve coupling efficiency between phosphoramidite reagents and alcohol substrates that are more sterically hindered or less reactive; suitable for parallel screening against tetrazole to compare the rate and extent of initial-stage bond formation.
Highly active tetrazole-type activator	21871-47-6	B115197	5-(Benzylthio)-1H-tetrazole	≥98.5%	Commonly used to enhance phosphoramidite coupling activity; suitable for further improving initial-stage conversion when tetrazole activation is insufficient, and for comparing how different activators affect substrate compatibility.
Highly active tetrazole-type activator	89797-68-2	E111310	5-(Ethylthio)-1H-tetrazole(ETT)	≥98%	Commonly used to accelerate phosphoramidite coupling; suitable for parallel comparison with tetrazole, 4,5-dicyanoimidazole, and 5-benzylthio-1H-tetrazole to identify a more suitable initial-stage activation system.
Mild post-oxidant	7553-56-2	I434868	Iodine	High purity, reagent grade, ≥99.8%(T)	Commonly used to oxidize the trivalent phosphorus intermediate formed in the initial stage into the pentavalent phosphorus product; suitable for establishing relatively mild and conventional post-oxidation conditions and for observing substrate tolerance to iodine-based oxidation systems.
Peracid oxidant	937-14-4	C106492	3-Chloroperoxybenzoic acid(MCPBA)	≥85%	Has relatively strong oxidizing power and is suitable for rapidly completing the conversion from trivalent phosphorus to pentavalent phosphorus; when the substrate contains oxidizable functional groups, selectivity and side reactions should be closely monitored.
Peroxide oxidant	75-91-2	T466691	tert-Butyl hydroperoxide solution	5.0-6.0 M in decane	Can be used to explore peroxide-based oxidation conditions for trivalent phosphorus intermediates; suitable for comparison with iodine and mCPBA to evaluate how different post-oxidation systems affect substrate stability and workup.
Hydrogen peroxide reference oxidant	7722-84-1	H112519	Hydrogen peroxide solution	ACS, 30 wt. % in H2O, contains stabilizer	With clearly defined composition and concentration, this can serve as a hydrogen peroxide reference oxidant for post-oxidation of trivalent phosphorus, enabling comparison of oxidation compatibility and workup differences under peroxide conditions; when used in phosphoramidite post-oxidation, the aqueous medium and stabilizer should also be taken into account in reaction setup and purification.

Table 3 | Final-Stage Debenzylation Components and Reference Reagents for Direct Pentavalent Phosphorus Routes

Category	CAS No.	Aladdin Catalog No.	Name	Grade or Purity	Product Features and Applications
Hydrogen donor for transfer hydrogenation	540-69-2	A432863	Ammonium formate	Anhydrous, reagent grade, ≥97%	Commonly used with palladium catalysts for transfer hydrogenolytic debenzylation; suitable for evaluating the feasibility of deprotection of dibenzyl-protected phosphate fragments without direct introduction of hydrogen gas.
Debenzylation catalyst	12135-22-7	P105997	Palladium hydroxide	AR	A commonly used debenzylation catalyst, suitable for final-stage deprotection of dibenzyl-protected phosphate esters; it can be used to verify whether the protected phosphate intermediate obtained in the initial stage can be smoothly released as the free phosphate.
Debenzylation catalyst	1314-15-4	P141419	Platinum oxide	Pt, 80-86%	A classical hydrogenation/hydrogenolysis catalyst, suitable for comparison with palladium hydroxide in order to evaluate debenzylation efficiency and substrate tolerance under different metal catalytic systems for dibenzyl-protected phosphate esters.
Mild reductive debenzylation reagent	617-86-7	T106570	Triethylsilane(NSC 93579)	≥98%	Can be used to screen milder debenzylation conditions; when conventional hydrogenolysis may affect double bonds, halogenated sites, or other reduction-sensitive functional groups, it can serve as a candidate reagent for evaluating alternative reductive conditions.
Classical chlorinated pentavalent phosphorylation reference reagent	10025-87-3	P475214	Phosphorus(V) oxychloride	PrimorTrace™, ≥99.99% metals basis	A classical chlorinated pentavalent phosphorylation reagent, suitable for comparison with the dibenzyl N,N-diisopropylphosphoramidite route in order to evaluate differences in substrate compatibility and step organization between classical highly reactive pentavalent phosphorylation pathways and protected routes of the type “trivalent phosphorus installation → oxidation → debenzylation.”

Note: The above are representative Aladdin products. For more product 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.

References

[1] Yu KL, Fraser-Reid B. A novel reagent for the synthesis of myo-inositol phosphates: N,N-diisopropyl dibenzyl phosphoramidite. Tetrahedron Letters. 1988;29(9):979-982. doi:10.1016/0040-4039(88)85313-9.

[2] Beaucage SL, Iyer RP. The synthesis of specific ribonucleotides and unrelated phosphorylated biomolecules by the phosphoramidite method. Tetrahedron. 1993;49(46):10441-10488. doi:10.1016/S0040-4020(01)81543-X.

[3] Beaucage SL. Oligodeoxyribonucleotides synthesis: Phosphoramidite approach. In: Agrawal S, ed. Protocols for Oligonucleotides and Analogs. Methods in Molecular Biology. Vol 20. Totowa, NJ: Humana Press; 1993:33-61. doi:10.1385/0-89603-281-7:33.

[4] Berner S, Mühlegger K, Seliger H. Studies on the role of tetrazole in the activation of phosphoramidites. Nucleic Acids Research. 1989;17(3):853-864. doi:10.1093/nar/17.3.853.

[5] Vargeese C, Carter J, Yegge J, Krivjansky S, Settle A, Kropp E, Peterson K, Pieken W. Efficient activation of nucleoside phosphoramidites with 4,5-dicyanoimidazole during oligonucleotide synthesis. Nucleic Acids Research. 1998;26(4):1046-1050. doi:10.1093/nar/26.4.1046.

[6] Domon K, Puripat M, Fujiyoshi K, Hatanaka M, Kawashima SA, Kanai M. Catalytic chemoselective O-phosphorylation of alcohols. ACS Central Science. 2020;6(2):283-292. doi:10.1021/acscentsci.9b01272.

[7] Ociepa M, Knouse KW, He D, Vantourout JC, Flood DT, Padial NM, Sanchez BB, Sturgell EJ, Chen JS, Baran PS. Mild and chemoselective phosphorylation of alcohols using a Ψ-reagent. Organic Letters. 2021;23(24):9337-9342. doi:10.1021/acs.orglett.1c02736.

[8] Hodson LE, Tholath PJ, Jacobs L, Pribut N, Pashikanti G, van der Westhuyzen AE, Laws DC III, Liotta DC. Mild and chemoselective triethylsilane-mediated debenzylation for phosphate synthesis. Organic Letters. 2025;27(1):246-251. doi:10.1021/acs.orglett.4c04258.