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Preparation of Auxiliaries for Asymmetric Syntheses from Tartaric Acid. Additions of Butyllithium to Aldehydes in Chiral Media. Chiral derivatives of the complexing 1,2‐diheterosubstituted ethanes A–D are prepared from tartaric acid. The key starting materials are the succinic acid derivative 1 , the dioxolane 2a , and the diamide 3a . These are converted to the ethers, alkoxyamines, and alkylthio‐amines listed in the first column of Table 2 which also contains the derivatives 21c, 22d , and 23d made from lactic acid, malic acid, and proline, respectively. It is shown that the highest optical yields (up to 40%) in reactions of butyllithium with aldehydes are obtained when mixtures of (−)‐1,2,3,4‐tetramethoxy‐butane ( 4b ), (+)‐2,3‐dimethoxy‐ N , N , N ′, N ′‐tetramethyl‐1,4‐butanediamine ( 17a ), and (−)‐1,4‐dimethoxy‐ N , N , N ′, N ′‐tetramethyl‐2,3‐butanediamine ( 14c ) with pentane are used at temperatures down to −150° and ratios of auxiliary/butyllithium of up to 10:1 (see equation (1), Tables 2–4).
Seebàch et al. (Wed,) studied this question.