Asymmetric aldol reactions using

Silvestri, G., Desantis, G., Mitchell, M. and Wong, C.-H. (2003) Asymmetric aldol reactions using aldolases. 

Sn(OTf)2 can function as a catalyst for aldol reactions, allylations, and cyanations asymmetric versions of these reactions have also been reported. Diastereoselective and enantioselective aldol reactions of aldehydes with silyl enol ethers using Sn(OTf)2 and a chiral amine have been reported (Scheme SO) 338 33 5 A proposed active complex is shown in the scheme. Catalytic asymmetric aldol reactions using Sn(OTf)2, a chiral diamine, and tin(II) oxide have been developed.340 Tin(II) oxide is assumed to prevent achiral reaction pathway by weakening the Lewis acidity of Me3SiOTf, which is formed during the reaction. 

Silvestri, M. G., Asymmetric Aldol Reactions Using Aldolases, 23, 267. 

A review of enantioselective aldol additions of latent enolate equivalents covers a variety of Sn", boron, Ti, Cu, lanthanide, and Lewis base catalysts. Asymmetric aldol reactions using boron enolates have been reviewed (401 references). ... 

Kiyooka S-i (1997) Development of a chiral lewis acid-promoted asymmetric aldol reaction using oxaborolidinone. Rev Heteroatom Chem 17 245-270... 

Scheme 1. The direct intermolecular asymmetric aldol reaction using L-proline.

Independently, Yamamoto, Yanagisawa, and others reported the asymmetric aldol reaction using trimethoxysilyl enol ethers.19 The reaction was conducted with aldehydes and trimethoxysilyl enol ethers in the presence of Tol-BINAP-AgF to give the corresponding adducts with high enantioselectivities and diastereoselectiv-ities. They obtained vyra-aldol adducts as major products even when silyl enol ethers derived from cyclic ketones were used. Moreover, when a,(3-unsaturated aldehydes were employed as substrates, 1,2 adducts were obtained exclusively (Table 9.10). From an NMR study and correlation between the E Z ratio of the enol ethers and diastereoselectiviy, they proposed a cyclic transition state (Fig. 9.5). Thus, the reaction of E enol ethers proceeded via a boat form, whereas the reaction of Z enol ethers took place via a chair form. 

C. J. Cowden, I. Paterson, Asymmetric Aldol Reactions Using Boron Enolates, Org. Prep. Proced. Int. 

Catalytic versions of the asymmetric aldol reaction using simple lithium enolates and substoichiometric amounts of a chiral catalyst are rare611. The bimetallic system proposed by Shibasaki and coworkers deserve to be mentioned at this point. The combination of a... 

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