Direct catalytic asymmetric synthesis of highly functionalized 2-methylchroman-2,4-diols via Barbas-list aldol reaction.

A practical and sustainable chemical process for the synthesis of highly substituted aldol<-->lactol products was achieved for the first time through the asymmetric Barbas-List aldol (BLA) reaction of 2-hydroxybenzaldehydes with acetone in the presence of a catalytic amount of trans-4-OH-L-proline (see scheme).