Tartaric acid-derived quaternary ammonium salts

Tartaric Acid-Derived Quaternary Ammonium Salts Starting from the freely available tartaric acid, Shibasaki et al. designed and prepared a series of diammonium salts by changing the acetal moieties (R and R ), aromatic parts (Ar), and counteranions (X) (Figure 12.11). Screening of the catalyst hbrary identified that catalyst 48a was efficient for the asymmetric alkylation of N-(diphenylmethylene) glycine tert-butyl ester [81] and that the C2-symmetric catalysts 48b, 49, and 50 were efficient for the conjugate addition [82]. 

Figure 12.11 Tartaric acid-derived quaternary ammonium salt phase-transfer catalysts.

Inspired by Maruoka s success in using axially chiral C2-symmetric binaphthyl-based N-spiro quaternary ammonium salts, both the Arai [83] and Waser [84] groups developed tartaric acid-derived N-spiro quaternary ammonium salts 51 and 52, respectively. These catalysts could promote the asymmetric alkylation and conjugate addition with good enantioselectivities. 

Generally, the chiral quaternary ammonium salts, derived from cinchona alkaloids [26, 28, 29, 46, 56-60] and C2-symmetric chiral binaphthyl or biaryl structures [61-68, 71-73, 77], were demonstrated to be very enantioselective catalysts for the asymmetric alkylation of 65a, and provided the corresponding chiral a-amino acids in over 95% ee in most cases. The tartaric acid-derived catalysts 48a [81] and 52 [84] and chiral guanidinium salts 53 [85] and 54 [86] were also found to be suitable for this alkylation reaction. However, in terms of catalytic activity, only a... 

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