BINOL derivatives phosphoric acid

In 2008, Toste and coworkers reported the desymmetrization of me o-episulfonium ions 131 generated in situ from ring closure of sulfides 132 featuring a P-trichloro-acetimidate leaving group [76], Chiral BINOL-derived phosphoric acid (5)-3o (15 mol%, R = triggered the formation of the intermediate mera-epi-... 

In 2008, the Ackennann group reported on the use of phosphoric acid 3r (10 mol%, R = SiPhj) as a Brpnsted acid catalyst in the unprecedented intramolecular hydroaminations of unfunctionaUzed alkenes alike 144 (Scheme 58) [82], BINOL-derived phosphoric acids with bulky substituents at the 3,3 -positions showed improved catalytic activity compared to less sterically hindered representatives. Remarkably, this is the first example of the activation of simple alkenes by a Brpnsted acid. However, the reaction is limited to geminally disubstituted precursors 144. Their cyclization might be favored due to a Thorpe-Ingold effect. An asymmetric version was attempted by means of chiral BINOL phosphate (R)-3( (20 mol%, R = 3,5-(CF3)2-CgH3), albeit with low enantioselectivity (17% ee). 

Until 2006, a severe limitation in the field of chiral Brpnsted acid catalysis was the restriction to reactive substrates. The acidity of BINOL-derived chiral phosphoric acids is appropriate to activate various imine compounds through protonation and a broad range of efficient and highly enantioselective, phosphoric acid-catalyzed transformations involving imines have been developed. However, the activation of simple carbonyl compounds by means of Brpnsted acid catalysis proved to be rather challenging since the acid ity of the known BINOL-derived phosphoric acids is mostly insufficient. Carbonyl compounds and other less reactive substrates often require a stronger Brpnsted acid catalyst. 

A BINOL-derived phosphoric acid derivative has been used as a catalyst in the enantioselective synthesis of a-amino phosphonates via hydrophosphonylation of imines with diisopropyl phosphite.82... 

A number of Bronsted acidic organocatalysts have been applied to the asymmetric hydrophosphonylation of aldimines. Thiourea catalysts related to (6.130) catalyse the asymmetric hydrophosphonylation of a range of aliphatic and aromatic aldimines with high ee and BINOL-derived phosphoric acid derivatives similar in structure to (6.131) are effective catalysts in the asymmetric phosphonylation of cinnamaldehyde-derived aldimines. Asymmetric hydrophosphonylation of aromatic aldimines can also be achieved with high ee using cheap, commercially... 

A chiral Lewis acid catalyst was prepared between the chiral BINOL-derived phosphoric acid (212) and Et2AlCl. In the presence of a catalytic amount of the A1 complex, the reaction between (i )-isocyanoacetamides (209) and aldehydes (210) afforded the corresponding enantio-enriched 2-(l-hydroxyalkyl)-5-aminooxazoles (211) in good yields and enantioselectivities (Scheme 59). ... 

In the absence of a catalytic amount of Lewis acids such as Mg(OTf)2, weak Bronsted acids, such as thioureas, BINOL, and BINOL-derived phosphoric acids, could not promote this reaction alone. The reaction could not proceed with phosphoric acid salts, suggesting that the use of free acid is essential for effective catalysis. The combination of chiral phosphoric acid 13e and Lewis acid Mgp2 (4 1 ratio) was identified to be the optimal catalyst for the AFC alkylation reactions of phenols with p,y-unsaturated a-keto esters, affording the alkylation product in good yields with up to 99% ee. Not only free phenols but also indoles could be successfully applied in AFC reactions with P,y-unsaturated a-keto esters under the binary-acid catalysis (82-94% ee). 

Simple aliphatic enones are also epoxidised with H2O2 using a preformed TFA or CI3CCO2H salt of 9-amino-9-deo gr-ep/-quinine (9-epi-QA), in up to 99% ee. The method was further expanded to a-monosubstituted and a,p-disubstituted enals, using preformed salts of 9-epi-QA with BINOL derived phosphoric acids. Also, epoxidation of 2-cyclopentenones was achieved by using C-2 phenyl-substituted 9-epi-QA in combination with (/ )-Mosher s acid as catalyst. ... 

BINOL-derived phosphoric acid 21.11 was also shown to catalyse addition of allyltrichlorosilane 21.5a to aldehydes. Methyl substituents in 3,3 ... 

Br0nsted Acid Organocatalysis. The field of Brpnsted add organo-catalysis [151] is clearly dominated by chiral binol-derived phosphoric acids, which after the seminal reports of Akiyama et al. [152] and of Uraguchi and Terada [153] have become one of the most powerful types of organic catalysts [154]. Figure 2.33... 

FIGURE 2.33. Chiral binol-derived phosphoric acids. 

Recently, Simon and Goodman have been able to develop a model, based on DFT calculations, that is able to predict the stereochemical outcome of more than 40 imine reactions catalyzed by binol-derived phosphoric acids (Figure 2.36) [156b]. The majority of nucleophilic additions to imines take place via a Type I transition state only if the R2 substituent of the imine is larger than R3 and if the nucleophilic atom is not on line with the OH bond (cf. additions of indoles or of ene carbamates to imines)... 

In general, binol-derived phosphoric acids are not good catalysts for the activation of simple carbonyl compounds such as aromatic, aliphatic, or a,p-unsaturated aldehydes or ketones [159]. In order to overcome these limitations, Nakashima and Yamamoto in 2006 [160] synthesized binol-derived A-trifyl phosphoramides (Figure 2.37). These compounds are 10 times more acidic than the corresponding phosphoric acids [157], a fact that can account for their higher catalytic efficiencies in reactions involving unsaturated ketones[160] or (3-keto esters [161]. 

FIGURE 2.35. Representative activation modes of binol-derived phosphoric acid. 

FIGURE 2.36. The Simon-Goodman transition state working models for the binol-derived phosphoric acid catalysis of nucleophilic additions to imines. 

Enantioselective reduction of ketones has been carried out using catecholborane and a BINOL-derived phosphoric acid the latter is suggested to be a pre-catalyst, with B-NMR evidence for the formation of a phosphoryl catechol borate as active 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. ... 

In 2009, Gong s group reported the dynamic kinetic transfer hydrogenation reaction of 2-methyl-2,4-diaryl-2,3-dihydrobenzo[ )][l,4]diazepines, using chiral phosphoric acids as organocatalysts and Hantzsch ester as the hydride source. ° A 3,3 -H8-BINOL-derived phosphoric acid was identified as the optimal chiral catalyst for this process, affording the corresponding 1,3-diamine derivatives with moderate diastereoselectivities of up to 78% de, and enan-tioselectivities of up to 94% ee, as shown in Scheme 2.107. 

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