Abstract 4,5,5‐Trisubstituted γ‐butyrolactones bearing two stereocenters including one quaternary carbon center have been synthesized in excellent yields via N‐heterocyclic carbene‐catalyzed annulations of enals and ketoesters. Chiral N‐heterocyclic carbenes were used to tune the diastereoselectivity up to an 83/17 cis / trans ratio and the enantioselectivity up to 78% ee ( trans isomer).
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Li et al. (2008) studied this question.