Synthesis of chiral chromenes from levoglucosenone

Levoglucosenone, an optically active alpha,beta-unsaturated ketone available from cellulose, undergoes a stereoselective oxa-Michael-aldol domino reaction with 2-hydroxybenzaldehydes with the formation of optically active oxepino[4,5-b]chromen-1-ones. These compounds attacked by nucleophiles undergo recyclization to 4-substituted oxepino[3,4-b]chromen-11a-ols, while their oximes treated with SOCl2 are converted to 3-cyano-2H-chromenes through the Beckmann fragmentation.