Organocatalyzed Michael–Michael Cascade Reaction:
Asymmetric Synthesis of Polysubstituted Chromans
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Abstract
An
enantioselective cascade Michael–Michael reaction between
chalcones enolates and nitromethane catalyzed by a bifunctional thiourea
is developed. This reaction provides a mild but efficient approach
to chiral benzopyrans bearing three consecutive stereocenters in high
yields with excellent stereoselectivities, and the benzopyrans can
be easily transformed to the corresponding tricyclic product