Practical Guide to Chiral Phosphoric Acid (CPA) Catalysis: Three Operating Modes, a Reaction Task Map, and a Troubleshooting/Selection Checklist (with Product Navigation and Product Tables 1–3)

I. Introduction: Why Can Chiral Phosphoric Acids (CPAs) Evolve from “Small-Molecule Acids” into a General Tool for Asymmetric Synthesis?

1.1 Background: What Is the “Core Contradiction” Asymmetric Synthesis Tries to Solve?

In the synthesis of drugs, natural products, and functional molecules, we often need to transform a substrate that is originally “left–right symmetric”—typically planar or freely rotatable—into a product that selectively favors just one enantiomer. Traditionally, this type of “chiral control” has relied on two major routes:

1. Chiral metal catalysis (a metal center plus a chiral ligand creates an asymmetric environment);

2. Chiral auxiliaries (introduce an auxiliary to create a chiral environment, then remove and recover it after the reaction; stereocontrol is achieved via extra “install/remove” operations).

However, many real-world substrates impose practical constraints: metal residues and the cost of ligand screening, functional-group sensitivity, harsh reaction conditions, and the burden of scale-up and purification.

Therefore, within organocatalysis, a particularly attractive direction is the following: can we use a metal-free, small-molecule catalyst to achieve high ee under mild conditions—while maintaining a broad reaction scope and good transferability across substrate classes? Chiral phosphoric acids are among the representatives that “broke out” under precisely this demand.

1.2 Definition: What Is a “Chiral Phosphoric Acid (Chiral Phosphoric Acid, CPA)”?

1. Chiral phosphoric acids (CPAs) typically refer to a class of chiral-framework phosphoric acid monoesters of phosphoric diesters (often written as (RO)₂P(=O)OH). The most classic and widely applied family is BINOL (1,1′-bi-2-naphthol)-derived axially chiral biaryl phosphoric acids. In reactions, these molecules serve as chiral Brønsted acid catalysts: they activate substrates via acidity/hydrogen bonding, and simultaneously use their own chiral spatial environment to determine from which face the reaction proceeds.

2. Historical landmark: In 2004, the Akiyama group (Angew. 2004) and the Uraguchi–Terada group (JACS 2004) reported—almost simultaneously—the highly efficient catalytic activity of BINOL-derived CPAs in asymmetric Mannich-type reactions. These are often regarded as the key starting point for the rapid expansion of CPA catalysis.

1.3 Why Are CPAs “Multifunctional”?

1. Noncovalent interactions are the main actors

CPAs do not “hold substrates” via metal coordination. Instead, they use hydrogen bonding, electrostatic interactions, and hydrophobic/steric organization to position the substrate toward a single, preferred pathway. This is why CPA catalysis is often summarized as “controlling stereoselectivity through noncovalent interactions.”

2. A “bifunctional” motif enables simultaneous activation

The phosphate group naturally provides both P–OH (acid / H-bond donor) and P=O (H-bond acceptor) interaction sites. Therefore, in many systems, a CPA can cooperatively organize an electrophile and a nucleophile within the same transition state.

3. 3,3′-Substituents = “pocket knobs”

For BINOL-CPAs, the most emphasized structural “knob” is the bulky aryl substitution at the 3,3′-positions. These substituents determine pocket size, how the substrate enters and orients, and which face is more accessible to attack. Many classic papers and reviews treat the 3,3′-effect as a central clue for understanding CPA selectivity.

II. How Does CPA Catalysis Actually Work? Three Typical Operating Modes

2.1 Why Are CPAs Naturally Suited for “Bifunctional” Catalysis?

The phosphate group in BINOL-CPAs contains both P–OH (acid / H-bond donor) and P=O (H-bond acceptor). Combined with the chiral spatial “pocket” formed by 3,3′-substituents, CPAs can both activate substrates and direct the attacking face through space and noncovalent interactions. This is the fundamental reason many reviews regard CPAs as a general chiral Brønsted acid platform.

2.2 Three Typical Operating Modes

Note: The following is a practical conceptual framework. Real systems may vary continuously along a spectrum of H-bonding ↔ weak protonation ↔ ion-pairing, and may switch with solvent/temperature/additives.

Operating mode	What the CPA is doing	Typical substrate/intermediate features	“Knobs” most sensitive for selectivity	Common misconceptions / troubleshooting points
Mode A: Hydrogen-bond clamping / bifunctional organization	Uses H-bonds like a “clip” to orient the substrate, while bringing nucleophile and electrophile into a favorable relative geometry	Substrate has a clear H-bond acceptor site; not necessarily fully protonated	3,3′ steric bulk; solvent competition for H-bonds; water content	Treating every CPA system as an “ion pair”—some systems are more H-bond-dominated
Mode B: Protonation → chiral ion pair (Chiral ion pair)	First turns the substrate into a stronger electrophile (e.g., iminium/oxocarbenium), then uses a “tight chiral counteranion pairing” to control which face is attacked	The reaction readily forms / requires stabilization of cationic species (iminium/oxocarbenium, etc.)	Solvent polarity (higher polarity more likely weakens pairing); temperature; acid strength	Focusing only on “how strong the acid is,” while ignoring solvent polarity—leading to ee fluctuation or collapse
Mode C: Chiral ion-pair interface / cooperative catalysis (possible involvement of metal phosphate)	CPA couples as a “chiral counteranion platform” with other activation modes (sometimes participating as a metal phosphate)	Metal salts/cationic catalytic centers are present, or the anionic environment needs to be programmed	Presence/identity of metal/salt; coordination and ionic strength; additives	Assuming “adding CPA always means purely organocatalytic”: in some systems the active species may be metal phosphate, not free CPA

Remark: In the literature, Mode B is often grouped under the ion-pair / chiral counteranion framework (counteranion-directed, ACDC). Mode C is often treated as CPA–metal/salt cooperation or the catalysis regime involving metal phosphates.

2.3 A “Minimum Diagnostic”: Which Mode Does My Reaction Resemble Most?

1. Does the reaction necessarily form / rely on a cationic intermediate? (iminium, oxocarbenium, benzyl-cation character, etc.)

Yes → prioritize understanding and optimizing via Mode B (ion pair).

2. Are there metal salts, Lewis acids, or conditions that clearly may generate a “metal phosphate”?

Yes → you must include Mode C in the mechanistic interpretation (some reactions have been explicitly validated for “metal phosphate vs free CPA” as the active species).

3. Does the substrate have strong H-bond acceptors and can be “oriented/activated” without strong protonation?

Yes → it often aligns more with Mode A (H-bond clamping).

4. Do changes in solvent polarity / water content cause large ee swings?

Yes → this often signals changes in ion-pair tightness or H-bond networks (corresponding to sensitive knobs in Mode B or Mode A).

Take-home message:

The essence of CPA is not merely “it is an acid,” but that it can use hydrogen bonding and ion pairing as handles to turn a reaction coordinate into a controllable chiral space.

III. What Can CPAs Be Used For? A Reaction Map Organized by Task

3.1 Quick Positioning by “Target Product Type / Key Stereocenter”

Task (target product)	Common substrates/intermediates	CPA’s dominant mode (typical)	Key point	Representative references
Build C–C / C–N bonds to generate N-containing stereocenters (β-amino carbonyls, chiral amine precursors, etc.)	Imines / protected imines (Mannich-type, etc.)	Mode B: protonation → chiral ion pair (common) or A (system-dependent)	Two pioneering 2004 papers brought BINOL-CPA to center stage (Mannich-type reactions)	Terada (JACS 2004); Akiyama (Angew. 2004)
“Mildly reduce” imines to chiral amines (asymmetric transfer hydrogenation / reduction)	Imines (especially ketimines) + Hantzsch esters (hydride donors)	Mode B: ion pair	Classic logic: CPA activates the imine (toward a more “iminium-like” reactive state), then enables enantioselective hydride transfer	Rueping et al. (Org. Lett. 2005)
Aldehyde allylation / crotylation → chiral alcohols (C–C bond formation)	Aldehydes + allyl boronates / related reagents	Often a boundary case between Mode A ↔ B (H-bond / protonation assistance + chiral environment control)	Practical rule of thumb: CPA can both “increase electrophilicity + provide a chiral approach face,” enabling high ee allylation-type transformations under mild conditions	Jain & Antilla (JACS 2010)
Friedel–Crafts alkylation/addition of electron-rich heteroarenes (indoles/pyrroles → chiral C–C bonds)	Indoles, pyrroles, etc. + electrophiles activatable by acid	Often Mode A or B (depending on whether stable cations / tight ion pairs are formed)	These reactions are highly “pocket-dependent”: matching 3,3′ sterics with the substrate often determines ee/rate	FC chemistry occupies a major part of CPA reviews;
Use CPA as a platform and couple with other catalytic modes (a more complex landscape)	Systems containing salts/metals/cooperative activation elements	Mode C: ion-pair/cooperative interface (some systems may behave as metal-phosphate-involving)	Key reminder: not every system “with CPA added” is equivalent to “free CPA catalysis”—cooperation/salt effects may redefine the active species	For a broader landscape, start with Terada’s review to build the panorama

3.2 Summary

1. The application landscape of CPA can be organized by the target stereocenter: N-containing stereocenters (Mannich/imine chemistry), chiral amines (transfer hydrogenation), chiral alcohols (aldehyde allylation), and heteroarene Friedel–Crafts C–C bond formation are among the most common “main battlefields.”

2. The three operating modes are not abstract theory: they map directly onto whether the substrate passes through ion pairing, whether the system is primarily governed by hydrogen-bond networks, and whether cooperative/ion-pair programming (including salt/metal effects) is in play.

IV. CPA Selection Knobs + Rapid Troubleshooting Checklist

4.1 Starting Point: First “Make the Reaction Work” with the Most Common Benchmark Catalysts

1. One of the BINOL-derived CPAs most frequently used in the literature as a general starting point is TRIP (3,3′-bis(2,4,6-triisopropylphenyl)-BINOL phosphoric acid).

2. The best CPA choice is highly substrate- and reaction-dependent, especially depending on whether the chemistry proceeds through imine/cationic intermediates and whether stereocontrol is dominated by noncovalent interactions vs ion-pairing.

4.2 Selection-Knob Table: Focus on the 5 Variables That Most Often Decide Success vs Failure

Knob (actionable variable)	Why it matters	How to tune it	Typical symptom
3,3′ substituents = “pocket size/shape”	Bulky substituents such as 3,3′-bisaryl often markedly improve enantioselectivity; the early Mannich work explicitly pointed out a significant beneficial effect of 3,3′ substitution on ee.	Low ee: prioritize switching to a CPA with a more “closed” pocket at 3,3′; too slow/no conversion: try a more “open” pocket or adjust solvent/temperature.	Very low ee but good conversion: often indicates pocket mismatch / insufficient organization.
Acidity and “ion-pair tightness”	In many CPA systems, stereocontrol relies on noncovalent interactions / chiral ion pairs, not simply “more acidic = faster.” How tight the ion pair is can directly reshape ee.	Strong background reaction: lower temperature / dilute / move toward conditions that favor a tighter ion pair; no conversion: moderately raise temperature or switch to a stronger activation pathway (but avoid starting with “a lot more acid” immediately).	ee highly sensitive to solvent/salt: often signals ion-pair-dominated control.
Solvent polarity (especially for ion-pair regimes)	The more polar the solvent, the more it can “pull apart” the ion pair, often causing ee to drop or fluctuate (particularly pronounced for ion-pair-type systems).	Low or drifting ee: try less polar solvents first; low conversion: then consider temperature/concentration/catalyst structure.	Large ee changes upon solvent switch with the same catalyst: suspect solvent polarity effects first.
Water/impurities/substrate purity (H-bond network + background reaction)	CPA selectivity often depends on H-bond/ion-pair networks; trace water and impurities can readily perturb the system (especially in imine-related reactions).	First run control experiments with dry conditions / fresh substrate / freshly prepared solvent, then discuss changing the catalyst.	Poor reproducibility: check this item first (more time-efficient than blindly swapping CPAs).
Salts/metals/additives (triggering “cooperation / counterion interface”)	In some systems, adding CPA may shift the active species toward a more complex counterion/cooperative regime; salts/metals can significantly change selectivity and rate.	If metal salts are present: run no-salt vs with-salt controls; if ee is abnormal: check whether salts were introduced unintentionally.	A small amount of salt causes abnormal ee/rate: indicates you are in a counterion-sensitive regime.

4.3 Rapid Troubleshooting Checklist: Three Failure Modes—What to Check First

A. No conversion / very low conversion

1. First check whether the substrate is activatable by CPA (many high-performing CPA reactions cluster around imines and related transformations that can be electrophilized / controlled via ion pairing).

2. Make the smallest possible change: raise temperature or increase concentration or slightly increase catalyst loading (change only one factor).

3. Then adjust structure: switch to a CPA with a more “open pocket” or change solvent (avoid changing three things at once).

B. Conversion occurs but ee is low

1. First switch the “pocket”: 3,3′ substitution is often the first and strongest handle for improving ee; early Mannich systems emphasized the strong positive contribution of 3,3′-bisaryl groups to ee.

2. Then tune solvent polarity (ion-pair tightness): in many systems, this is the primary knob controlling ee.

3. Then lower temperature / suppress background reaction (sometimes low ee is not “the wrong CPA,” but rather “background reaction diluting ee”).

C. ee/yield fluctuates; reproducibility is poor

1. First run a water/impurity control (fresh solvent / drying / freshly prepared substrate).

2. Then confirm the catalyst’s own enantiopurity/state. When reproducibility is poor, the catalyst itself must be checked—for example, ^31P NMR can be used to assess hydrolysis/degradation/impurity peaks. If you want to use NMR to evaluate CPA enantiopurity, it typically requires introducing a chiral discriminating agent (e.g., a chiral amine) to form resolvable signals, followed by quantification.

3. If you mainly do imine-related nucleophilic additions (Mannich/additions to N-Boc imines, etc.), you may use a literature-rule-based CPA selection tool (e.g., BINOPtimal) to reduce blind trialing. However, its rules largely cover BINOL-CPA + imine/nucleophile transformations. Outside that domain, it is still recommended to return to the “minimum diagnostic” in 2.3 (identify Mode A/B/C first) and the evidence-chain logic in 4.2–4.3 (knobs/control experiments), and only then decide whether to switch CPA or switch scaffold.

V. Product Selection Navigation Table | Chiral Phosphoric Acid (CPA) Catalysis: Locate Tables 1–3 by “Experimental Task”

Need / scenario (typical experimental or methodological question)	Which table to check first	Why this table first	What you can quickly extract from it
I haven’t started CPA yet and don’t know where to begin; I want to first make the reaction work and establish a baseline (conversion/ee/byproduct profile).	Table 2	BINOL-family CPAs (baseline + 3,3′ substitution)	Table 2 covers the most commonly used “general starting tiers”: from baseline CPAs (as controls) to key screening workhorses such as TRIP, then further tuning by sterics/π-systems/electronics—ideal for a workflow of make it work → optimize.
New reaction/new substrate: I need to quickly identify the stereochemical sense (R vs S product) and lock the ee ceiling as early as possible.	Table 2	BINOL-family CPAs (baseline + 3,3′ substitution)	Within the same series, Table 2 often provides both R/S enantiomers and multiple “pocket shapes,” enabling you to determine stereochemical sense + pocket type with minimal experiments.
The reaction runs, but ee is insufficient / selectivity is unstable; I suspect stronger pocket enclosure or larger sterics are needed to suppress background reaction.	Table 2	BINOL-family CPAs (3,3′ steric / ultra-bulky)	3,3′ substitution is the most central “knob” in CPA selectivity: increasing enclosure can suppress background pathways and improve ee—often the most common route from “feasible” to “high ee.”
The substrate is aromatic, or you suspect the transition state relies on π–π / CH–π recognition (aromatic substrates, clear ion-pair control); you want to enhance recognition using a “π pocket.”	Table 2	BINOL-family CPAs (large π-aryl: phenanthryl/anthryl)	π-aryl substituents are often used to strengthen hydrophobic enclosure and π recognition; in some aromatic and ion-pair-dominated systems they can markedly improve ee/regioselectivity.
Substrate reactivity is low and the reaction is slow; I suspect stronger acidity / stronger H-bond–ion-pair activation is needed (but I worry about side reactions).	Table 2	BINOL-family CPAs (electron-withdrawing: bis-CF₃)	Electron-withdrawing substituents tend to increase acidity and ion-pair strength—commonly used when “reactivity is insufficient,” while requiring closer attention to background/side-reaction windows.
BINOL tuning still doesn’t work (ee won’t rise / poor matching / need a deeper, larger 3D chiral space); I want to switch to a “large scaffold + deep pocket” route.	Table 3	VAPOL/VANOL family (large scaffold pocket)	VAPOL/VANOL are a classic alternative CPA family: larger scaffold and deeper pocket, often used to break BINOL’s substrate boundary or provide a different recognition mode.
I want to synthesize/derive CPAs myself (or do mechanistic controls/custom substitution), and need to first prepare the diol scaffold and phosphorylation reagents.	Table 1	Synthetic precursors & key reagents (diol scaffolds + POCl₃)	Table 1 provides the key inputs for building CPAs from the source: R/S or racemic precursors of BINOL/H8-BINOL/SPINOL, plus common phosphorylation reagents—ideal for self-prep/customization/scale-up routes.
Methodology/mechanistic work requiring strict controls: distinguish “scaffold effects (BINOL vs H8 vs SPINOL vs VAPOL)” from “3,3′ substitution effects.”	Table 2 + Table 1 + Table 3 (in this order)	Start with Table 2 to establish structure–selectivity relationships within the same scaffold by varying 3,3′; then switch scaffolds using Table 1 (H8/SPINOL) for scaffold controls; finally use Table 3 to test whether “large scaffold deep pocket” changes the recognition mode.	A systematic “knob library” for controlled comparisons: 3,3′ sterics/π/electronics (Table 2) + different diol scaffolds (Table 1) + large-scaffold pockets (Table 3).
Scale-up/process-window exploration: worried about ee drift, batch variation, and impurity/enantiopurity impacts on catalytic performance.	Table 2 (CPAs with ee stated) + Table 3 (ee stated)	Scale-up and reproducibility are more sensitive to catalyst enantiopurity and batch consistency; entries with ee stated are more suitable for reliable screening and reproduction.	CPAs in Table 2/3 labeled ≥99% (ee) (e.g., VAPOL/VANOL, some large-π CPAs), enabling robust selection for demanding systems.

Practical tip for use:

Priority strategy for new systems: first use Table 2’s “baseline + TRIP (R/S)” to make the reaction work and determine stereochemical sense; then switch by problem type to “larger sterics / π systems / stronger acidity.” If still not ideal, move to Table 3 for scaffold-level replacement. Return to Table 1 when you need self-prep/customization and must stock the diols and phosphorylation reagents.

Table 1 | Synthetic Precursors & Key Reagents (Diol Scaffolds + Phosphorylation Reagents)

Category	CAS No.	Aladdin Cat. No.	Name	Specification / Purity	Product features & applications (CPA-related)
Precursor | BINOL diol scaffold (core diol for CPA synthesis)	18531-94-7	B107539	(R)-(+)-1,1′-Bi-2-naphthol	≥99%	Classic BINOL chiral diol parent scaffold; commonly used to prepare BINOL-derived chiral phosphoric acids (CPAs; essentially cyclic hydrogen phosphates bearing P–OH) and derivatives; also used as a ligand/chiral building block. The R configuration corresponds to one chiral pocket type (opposite enantioselectivity to the S form).
Precursor | BINOL diol scaffold (core diol for CPA synthesis)	18531-99-2	B100620	S-BINOL	≥99%	High-purity S-BINOL precursor: suitable for direct preparation of S-configured BINOL-CPAs (cyclic hydrogen phosphates bearing P–OH), enabling rapid access to the “opposite stereochemical direction” catalyst library.
Precursor | BINOL diol scaffold (racemic/unresolved; control or precursor)	602-09-5	B114382	1,1′-Bi-2-naphthol	≥99%	Not labeled as enantiopure (often used as racemic/unresolved BINOL/control): can be used to prepare racemic or unlabeled BINOL-CPA, or as a synthetic precursor; if a single-enantiomer CPA is needed, resolution or direct purchase of (R)/(S)-BINOL is typically required.
Precursor | H8-BINOL (hydrogenated BINOL) diol scaffold	65355-14-8	R139148	(R)-(+)-5,5′,6,6′,7,7′,8,8′-Octahydro-1,1′-bi-2-naphthol	≥97%	Used to construct H8-BINOL-CPAs: compared with BINOL, the steric geometry/conformation and electronic environment differ, often enabling substrate matching and selectivity tuning (switching scaffolds can sometimes significantly change ee/rate/side reactions for the same transformation).
Precursor | H8-BINOL (hydrogenated BINOL) diol scaffold	65355-00-2	S139146	(S)-(–)-5,5′,6,6′,7,7′,8,8′-Octahydro-1,1′-bi-2-naphthol	≥97% (HPLC)	S-configured H8-BINOL: used to prepare S-configured H8-BINOL-CPAs or as a chiral building block; paired with the R form to rapidly switch stereochemical output direction.
Precursor | SPINOL diol scaffold (spiro, high rigidity)	223259-62-9	R300597	(R)-2,2,3,3-Tetrahydro-1,1-spirobi[1H-indene]-7,7-diol	≥99%	SPINOL diol for SPINOL-CPA synthesis: the spiro framework is more rigid and geometrically “compact,” often used for high-ee systems; a commonly used CPA scaffold route alongside BINOL/H8-BINOL.
Precursor | SPINOL diol scaffold (spiro, high rigidity)	223259-63-0	S300598	(S)-2,2,3,3-Tetrahydro-1,1-spirobi[1H-indene]-7,7-diol	≥98%	S-configured SPINOL diol: used to construct the opposite enantiomer of SPINOL-CPA; mirror-related to the R form, enabling systematic screening and rapid switching of stereochemical direction.
Key reagent | Phosphorylation/chlorinating reagent (for preparing phosphoric acids/phosphates)	10025-87-3	P475214	Phosphorus oxychloride(V) (POCl₃)	PrimorTrace™, ≥99.99% metals basis	Common phosphorylation reagent: a key reagent for converting diols such as BINOL/H8-BINOL/SPINOL into chiral phosphoric acid frameworks (cyclic hydrogen phosphates bearing P–OH). Ultra-high metals-basis purity suits trace-metal-sensitive catalysis/mechanistic studies. Note: strongly corrosive, highly exothermic; strictly anhydrous conditions and rigorous safety procedures required.

Table 2 | BINOL-Family CPAs (Baseline + 3,3′ Substitution; Grouped by “Sterics / π System / Electronic Effects”)

Category	CAS No.	Aladdin Cat. No.	Name	Specification / Purity	Product features & applications (CPA-related)
CPA | BINOL baseline (no ultra-bulky 3,3′ substitution; control / initial screening)	39648-67-4	B107410	(R)-(–)-BINOL phosphoric acid	≥98%	Baseline BINOL-CPA (essentially a cyclic hydrogen phosphate bearing P–OH) used as a chiral Brønsted acid catalyst/control: suitable for initial screening / condition scouting; often used for H-bond/ion-pair activation of substrates such as imines/acetals/enamines (e.g., Mannich, Pictet–Spengler, acetalization/rearrangements as general starting points).
CPA | BINOL baseline (no ultra-bulky 3,3′ substitution; control / initial screening)	35193-64-7	B117618	(S)-(+)-BINOL phosphoric acid	≥97%	S-configured version of the baseline CPA (cyclic hydrogen phosphate bearing P–OH): useful as a general starting point/control and for obtaining the opposite enantiomeric product; highly practical for feasibility checks in new systems.
CPA | BINOL baseline (racemic/unlabeled enantiomer; control/baseline)	35193-63-6	B120028	BINOL phosphoric acid	≥99%	Baseline BINOL-CPA (cyclic hydrogen phosphate bearing P–OH; enantiomer not specified; often used as a baseline control): suitable for baseline catalyst testing and reaction-window scouting; also commonly used to compare with 3,3′-substituted CPAs to determine whether stronger sterics/stronger acidity is needed.
CPA | 3,3′-steric aryl substitution (TRIP type, 2,4,6-triisopropylphenyl)	791616-63-2	R189216	(R)-3,3′-Bis(2,4,6-triisopropylphenyl)-1,1′-binaphthyl-2,2′-phosphoric acid	≥98%	Typical general high-performance CPA (TRIP type): 3,3′ sterics and acidity sit in a widely useful “sweet spot,” often a top-priority screening point for asymmetric Brønsted acid catalysis. Note: the chemistry is still a single cyclic hydrogen phosphate (P–OH), not “two phosphoric acid groups.”
CPA | 3,3′-steric aryl substitution (TRIP type, 2,4,6-triisopropylphenyl)	874948-63-7	S464538	(S)-3,3′-Bis(2,4,6-triisopropylphenyl)-1,1′-binaphthyl-2,2′-phosphoric acid	≥98%	S-configured version of the widely used steric aryl CPA: ideal as a workhorse for make it work → fine-tune workflows; often used to quickly establish ee and then optimize solvent/temperature/concentration (cyclic hydrogen phosphate bearing P–OH).
CPA | 3,3′ ultra-bulky aryl substitution (cyclohexylphenyl)	1359764-39-8	H299325	(R)-3,3′-Bis(2,4,6-cyclohexylphenyl)-BINOL phosphoric acid	≥98%	Extremely bulky aryl substitution forming a more closed pocket: often used for difficult-to-discriminate substrates or systems with competing pathways to improve ee and regio-/diastereocontrol (cyclic hydrogen phosphate bearing P–OH; more sensitive to solvent/concentration windows).
CPA | 3,3′ super-bulky substitution (silyl: triphenylsilyl)	791616-55-2	R281857	(R)-(–)-3,3′-Bis(triphenylsilyl)-BINOL phosphoric acid	≥98%	Super-bulky silyl groups at 3,3′ (commonly triphenylsilyl-type) deepen/tighten the chiral pocket: often used to raise enantioselectivity and suppress background reactions; also useful for fine control with sterically sensitive substrates (watch solubility/mass transfer). Cyclic hydrogen phosphate bearing P–OH.
CPA | 3,3′ super-bulky substitution (silyl: triphenylsilyl)	929097-92-7	B299329	(S)-3,3′-Bis(triphenylsilyl)-BINOL phosphoric acid	≥99%, ≥98% (ee)	S-configured super-bulky CPA: for extreme stereocontrol and background-reaction suppression; ee stated supports reliable screening in demanding asymmetric reactions (low loading/complex substrates). Cyclic hydrogen phosphate bearing P–OH.
CPA | 3,3′ large π-aryl substitution (phenanthryl)	864943-22-6	B300911	(R)-3,3′-Di(9-phenanthryl)-BINOL phosphoric acid	≥98%, ≥99% (ee)	Large π system (phenanthryl) can enhance π–π/CH–π recognition and hydrophobic enclosure; often helpful for aromatic substrates and ion-pair-controlled reactions; suitable for “high-selectivity CPA” screening tiers. Cyclic hydrogen phosphate bearing P–OH.
CPA | 3,3′ large π-aryl substitution (phenanthryl)	1043567-32-3	B299741	(S)-3,3′-Di(9-phenanthryl)-BINOL phosphoric acid	≥98%	S-configured phenanthryl CPA: for paired control and stereochemical-direction switching; an option within high-ee catalyst libraries for aromatic/ion-pair-controlled reactions. Cyclic hydrogen phosphate bearing P–OH.
CPA | 3,3′ large π-aryl substitution (anthryl)	361342-51-0	I169905	(R)-3,3′-Bis(9-anthryl)-BINOL phosphoric acid	≥95%	Anthryl provides a larger π surface and steric volume: useful for substrates/transition states sensitive to π recognition/stacking; often used as an extension set for “maximum ee / special substrate matching.” Cyclic hydrogen phosphate bearing P–OH.
CPA | 3,3′ large π-aryl substitution (anthryl)	361342-52-1	I169906	(S)-3,3′-Bis(9-anthryl)-BINOL phosphoric acid	≥98%	S-configured anthryl CPA: for opposite stereochemical output; commonly screened as an R/S pair to quickly determine optimal stereochemical direction and ee ceiling in π-recognition-driven systems. Cyclic hydrogen phosphate bearing P–OH.
CPA | 3,3′ electron-withdrawing substitution (bis-CF₃; increased acidity)	791616-62-1	B299327	(R)-3,3′-Bis[3,5-bis(trifluoromethyl)phenyl]-BINOL phosphoric acid	≥98%	Electron-withdrawing groups often increase acidity and alter H-bond/ion-pair strength: potentially advantageous for low-reactivity substrates requiring stronger activation; also watch for amplified side/background reactions. Cyclic hydrogen phosphate bearing P–OH.
CPA | 3,3′ electron-withdrawing substitution (bis-CF₃; increased acidity)	878111-17-2	B299328	(S)-(+)-3,3′-Bis(3,5-bis(trifluoromethyl)phenyl)-BINOL phosphoric acid	≥98%	Mirror enantiomer of the corresponding R form: used to obtain the opposite enantiomeric product; often paired in screening to quickly lock stereochemical direction. Cyclic hydrogen phosphate bearing P–OH.

Table 3 | VAPOL/VANOL Family CPAs and Related Phosphorus-Containing Scaffolds (Large-Scaffold Pockets)

Category	CAS No.	Aladdin Cat. No.	Name	Specification / Purity	Product features & applications (CPA-related)
CPA | VAPOL/VANOL chiral phosphoric acids (large-scaffold pocket)	871130-18-6	H282302	(R)-(–)-VAPOL phosphoric acid	≥98%, ≥99% (ee)	VAPOL-family CPAs are large-scaffold, deep-pocket chiral phosphoric acids: they can be distinctive when stronger enclosure/recognition is required or when BINOL systems give insufficient ee/reactivity. The ee label highlights that catalyst enantiopurity is crucial for catalytic outcome and scale-up reproducibility. Cyclic hydrogen phosphate bearing P–OH.
CPA/derivative | VAPOL/VANOL family phosphorus-containing scaffold	871130-17-5	H282303	(8aS)-18-Hydroxy-8,9-diphenyl-18-oxide-dinaphthopyrroline[4,3-d:3″,4″-f][1,3,2]dioxaphosphorin	≥98%, ≥99% (ee)	A VAPOL/VANOL-family phosphorus-containing large-scaffold compound (often used as a building unit, control, or library-expansion option in CPA-related chemistry). It can be an important alternative when deeper chiral space and stronger shape recognition are needed. The ee label indicates enantiopurity can strongly impact results in methodology screening or scale-up.
CPA | VAPOL/VANOL chiral phosphoric acids (large-scaffold pocket)	175223-61-7	H282305	(S)-VANOL phosphoric acid	≥98%, ≥99% (ee)	VANOL-family CPA: same family as VAPOL but with different scaffold geometry and potentially different substrate matching; often used to expand the reaction space where BINOL systems “don’t work” or deliver insufficient ee, as an important scaffold alternative. Cyclic hydrogen phosphate bearing P–OH; enantiopurity is critical for performance and reproducibility.

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