Practical Synthesis of Chiral Building Blocks by Highly Efficient Catalytic Asymmetric Acylation

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Recently, much attention has been focused on the non-enzymatic asymmetric acylation of racemic alcohols and meso-diols. We have already demonstrated asymmetric acylation of racemic secondary alcohols and meso-l,2-diols by the reaction with achiral benzoyl halide in the presence of a catalytic amount of chiral 1 , 2-diamine derived from (S)-proline. Some papers, which are based on the catalytic asymmetric acylation of alcohols with achiral acylating agents , have emerged successively in recent years. However, neither methodology has been developed to such a level as to find widespread use in organic synthesis.We established that a chiral 1,2-diamine derived from (S)-proline could function as a highly efficient catalyst for the catalytic asymmetrization of meso- l , 2-diols. Catalytic asymmetric acylation of cw-2-cyclopentene- l ,4-diol has been successfully performed by the reaction with benzoyl chloride in the presence of 0. 5 mol% of chiral diamine combined with a stoichiometric amount of triethylamine to give the corresponding monobenzoate with excellent enantioselectivity. Thus obtained 4-benzoyloxy-2-cyclopenten-l-ol was readily converted to (R)-4-benzoyloxy-2-cyclopenten-1-one, a chiral building block for various prostaglandins, by the treatment of pyridinium dichromate (PDC). Catalytic asymmetric acylation of meso-1, 3-diols has been also successfully performed in the presence of only 0.5 mol% of chiral 1,2-diamine, combined with 1.5 equivalents of triethylamine. Catalytic kinetic resolution of racemic primary alcohols has been also performed with substituted benzoyl chloride in the presence of only 0.3 mol% of chiral 1,2-diamine derived from (S)-proline. This highly efficient asymmetric acylation of alcohols afforded various useful chiral building blocks.