Organocatalysis in Synthesis: L-Proline as an Enantioselective Catalyst in the Synthesis of Pyrans and Thiopyrans

摘要

The multicomponent reaction (MCR) of aromatic aldehydes >1 and malononitrile (>2) with active methylenes >5a–h in the presence of L-proline produced pyrans and thiopyrans >6a–h stereospecifically and in good yields. Moreover a novel MCR of ethyl propiolate (>8) with >1 and >2 in the presence of L-proline to afford (R)-polysubstituted pyran is also reported. X-ray structures, e.e. and optical activity of the synthesized compounds indicated that L-proline as a catalyst is responsible for the observed enantioselectivity in the studied reactions.