BINOL phosphoric acid catalyst

A related reaction involves the use of aryl indole-3-carbinols with enamides. Under the influence of acid catalysts the carbinols generate electrophiles. The adducts hydrolyze to products that are the equivalent of conjugate addition to 1,3-diaryl propenones. These reactions can be done in up to 90% ee with chiral BINOL-phosphoric acid catalysts [293]. 

Calculations suggested that the Strecker reaction of iV-aryl imines catalyzed by the BINOL-phosphoric acid catalyst (124) proceeded through transition states in which the catalyst simultaneously bound both the imine and the nucleophile (Scheme 35). ... 

Similarly, using BINOL phosphoric acid catalyst 191, Hiemstra and co-workers developed an organocatalytic Pictet-Spengler (PS) reaction of tryptamine derivative 189 and 4 -oxo-pentanal 190 as a key step to achieve the key intermediate 192 (86% yield, 89% ee), which was then converted to (—)-arboricine (193) [78] by a sequence of reactions including diasteroselective Pd(0)-catalyzed iodoalkene-enolate cycUza-tion (33% overall yield, 6 steps) (Scheme 17.32) [79]. Importantly, only 1 mol% loading of catalyst 191 on a 10 mmol Pictet-Spengler (PS) reaction scale gave the compound 192 in 92% yield, but with relative low enantioselectivity (78% ee). 

A hydroamination/N-sulfonyliminium cyclization cascade was carried out enantioselectively with gold and BINOL-phosphoric acid catalysts to generate fused indole 188. The method can also be extended to furnish lactams with up to 93% ee (13OL4330). Polycyclic indoline 189 was prepared via an indium/TFA-catalyzed tandem cycloannulation of P-oxodithioesters with tryptamine in yields up to 92% (130L1974). Dixon and colleagues utilized an enantioselective Michael addition/iminium ion cyclization of trypt-amine-derived ureas in the synthesis of tetracyclic indole 190 (22 examples, up to 78% yield and 96% ee) (130L2946). 

The good enantio- and regioselectivity can be explained through transition state TS-6 where the azomethine ylide and the methyleneindolinone build hydrogen bonds with the chiral BINOL-phosphoric acid catalyst 239 (Fig. 6.10). 

Enantioselective versions of the Hantzsch reaction have also been reported. As shown in Scheme 3.2, the reaction between dimedone, ethyl acetoacetate, ammonium acetate, and aromatic aldehydes in the presence of a chiral BINOL-phosphoric acid catalyst 7 gave compounds 8 in good to excellent yields and in enantiomeric excesses above 94%, although the absolute configuration of the final products was not determined [10]. 

Examining a variety of chiral BINOL based phosphoric acid catalysts in 2005, List found TRIP (Scheme 7.4) to be optimal (1.0mol%) for the catalytic protonation of preformed imines of p anisidine [15]. 

In 2008, Du and coworkers designed and synthesized novel double axially chiral phosphoric acid catalysts based on BINOL [28]. Subsequently, these catalysts have been successfully applied in asymmetric transfer hydrogenation of 2 substitued (Table 10.8) and 2,3 disubstitued quinolines (Scheme 10.26). They found that ether was the best solvent. For 2 substitued quinolines, up to 98% ee was obtained when the substitutent of catalyst was cyclohexanyl. 

Several chiral catalysts for conjugate addition have been explored, including both protic and Lewis acids. 3,3 -hri-(4-Nitrophenyl)-BINOL-phosphoric acid gives 40-98% yields and 40-55% ee with p-aryl enones [243]. 

The chiral catalysts that have been used in nitroaUcene conjugate additions include bw-oxazolines with Cu(OTF)2 [281] or Zn(OTf)2 [282], tridentate bw-oxazolines with Zn(OTf)2 [283], mixed thiazoline-oxazolines with Zn(OTf)2 [284], imidazoUne-aminophenols with CuOTf [285], bis-trifluoromethylsulfonamides [286], binaphthyl sulfonamides [287], binaphthyl imines [288], thioureas [289], and quinoUnyl thioureas [290]. A BINOL-phosphoric acid with 3A molecular sieves gave ee values consistently at 90% and above with both p-alkyl and p-aryl nitroalkenes [291]. 

Excellent enantioselectivity has also been obtained using 3,3 -6 s-(l-naphthyl) BINOL-phosphoric acids [311]. A -Tosyl imines of aryl aldehydes were also examined using a binaphthyl Pd(II) carbene complex as the catalyst. Enantioselectivity in the 50-75% range was obtained [312]. Imines formed from ot-phenylethylamine and ethyl 3,3,3-trifluoropyruvate give adducts with 85-97% de in the presence of TEA [313]. The chiral auxiliary can be removed by hydrogenolysis. 

Concurrently, the group of Akiyama reported the use of the rather similar (/ )-BINOL-based phosphoric acid catalyst 76g [48]. A selection of aldimines 78a-d was reacted with silyl ketene acetals 79a-b to give rise to the p-amino esters 8 a-d in good dr (>86 14 iyn-selectivity) and high ee (np to 96%, Scheme 5.37). 

Therefore an efficient substrate recognition site could be constructed around the activation site of the phosphoric acid catalyst, namely the acidic proton, as a result of the acid/base dual function and stereoelectronic influence of the substituents (STG). The BINOL derivatives were selected as chiral sources to construct the ring structure The C2 symmetry is crucial in the catalytic design because it means that the same catalyst molecule is generated when the acidic proton migrates to the phosphoryl oxygen. In addition, both enantiomers of the binaphthols are commercially available [52]. 

Later on, the Rueping group reported an organocatalytic enantioselective reduction of pyridine 180 (Scheme 17.30) [74], according to the procedure described by Bohlmann and Rahtz [75]. The key step in the synthesis of decahydroquinolines from the pumiliotoxin family involved Hantzsch dUiydropyridine 172 as the hydride source and involved BINOL-phosphoric acid 181 as a chiral Br0nsted acid catalyst... 

Two reports concern enantioselective Baeyer-Villiger (BV) reactions. Oxidation of 2,3,4-trisubstituted cyclobutanone (154) has been performed in high yield and ee with a BINOL-derived phosphoric acid catalyst, using aqueous hydrogen peroxide as oxidant many other cyclobutanone examples are also described. ... 

Gong s group reported the first catalytic enantioselective Biginelli-like reaction [46, 47] using cyclic and acyclic ketones (33 and 35, respectively), instead of p-ketoester and a BINOL-based phosphoric acid catalyst 34 (Scheme 9.10 and Fig. 9.2). 

An a/ -stereo- and diastereo-selective glycosylation method employs a glucosyl a-trichloroacetimidate and a chiral BINOL-derived phosphoric acid catalyst the system selects the i -enantiomer of a racemic mixture of secondary alcohols. ... 

DFT has been employed to probe the mechanisms of chiral BINOL-phosphoric-acid-catalysed allylboration and propargylation reactions, with a particular focus on whether the catalyst interacts with the pseudo-axial or pseudo-equatorial oxygen of the boronate. °... 

Strained allylic cyclobutanols and cyclopropanols undergo ring expansion promoted by a chiral binol-derived phosphoric acid catalyst to give 0-fluoro spiroketone products (Scheme 80). ... 

An insoluble cationic iodinating reagent, combined with a chiral binol-derived lipophilic phosphoric acid catalyst, has been found to act as an efficient source of chiral iodine that performs the semipinacol transposition of strained allylic alcohols to -iodo spiroketones B (Scheme 85). (Se)... 

Spirocyclic phosphoric acid catalyst STRIP (6) turned out to be crucial in the development of the kinetic resolution of homoaldols. The SPINOL backbone outperformed a variety of other previously described phosphoric acids based on BINOL (3 and 2), H8-B1NOL (9), VAPOL (1), and TADDOL (10) backbones (Table 2). 

In the second reaction, a Michael-Michael cascade between an unsaturated oxin-doles 17 and enones 22 was shown to be catalyzed by a primary amine-derived catalyst (II) (Scheme 10.3). The reaction afforded the spirooxindoles 23 in excellent yields and diastereo and enantioselectivities. Wang used a similar approach in the reaction of isatylidene malononitriles and enones [12]. The reaction was catalyzed by the dual combination of cinchona-based chiral primary amine and BINOL phosphoric acids to afford the spirocycles in excellent yields (88-99%), diastereo (up to 99 1 dr), and enantioselectivities (95-99% ee). 

BINOL-derived phosphoric acid catalyst affording the P-amino ketone (231) in 96% yieldand92% ee (Scheme 11.51) [156]. The total synthesis of (-)-anabasine (232) was completed in three more steps in 55% overall yield (i) reduction of the conjugated double bond, (ii) lednction of the ester moiety with an excess DIBAL-H resulting in the formation of the piperidine ring, and (iii) removal of the PMP-protective group. 

A purely ionic hydrogen bond activation mechanism might be involved in the aza-Henry reaction between a-iminoesters, a very reactive subclass of imines, and various nitroalkanes catalyzed by the BINOL phosphoric acid 44 [54]. The corresponding P-nitro-a-amino acid esters were produced in good yields, diastereo- and enantioselectivities (Scheme 29.23). The authors postulated a dual role of catalyst 44 through activation of the a-iminoester by protonation and control over the nitroaUcane/nitronate equilibrium (Scheme 29.24). 

---