2-Butanol, 2-phenyl-, asymmetric synthesis

As early as 1977 Pracejus et al. investigated alkaloid-catalyzed addition of thiols to a-phthalimido acrylates, methylene azlactones, and nitroolefins [56a]. In the former approach, protected cysteine derivatives were obtained with up to 54% ee. Mukaiyama and Yamashita found that addition of thiophenol to diisopropyl mal-eate in the presence of cinchonine (10 mol%) proceeds in 95% yield and that the product, (S)-phenylthiosuccinate, was formed with 81% ee [56b]. The latter Michael adduct was used as starting material for preparation of (R)-(+)-3,4-epoxy-1-butanol. In the course of an asymmetric total synthesis of (+)-thienamycin Ike-gami et al. studied the substitution of the phenylsulfonyl substituent in the azetidi-none 69 by thiophenol in the presence of cinchonidine (Scheme 4.34) [56c]. This substitution probably proceeds via the azetinone 70. In this reaction the phenyl-thioazetidinone 71 was obtained in 96% yield and 54% ee. Upon crystallization, the optically pure substitution product 71 was obtained from the mother liquor... 

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