Stereocontrolled organocatalytic strategy for the synthesis of optically active 2,3-disubstituted cis-2,3-dihydrobenzofurans.

An intramolecular, organocatalyzed Michael addition has been developed to obtain biologically important 2,3-disubstituted cis-2,3-dihydrobenzofurans. By using mandelic acid salts of primary aminocatalysts, derived from cinchona alkaloids, the intramolecular cyclization reaction has been developed to proceed in high yield, with moderate to good diastereoselectivity, and up to 99% ee. Based on the absolute configuration of the formed 2,3-disubstituted-cis-2,3-dihydrobenzofurans and by considering the observed substrate scope restrictions, a mechanistic rationalization has been presented.