A stereocontrolled route to 2-substituted chromans

A two-step synthesis of 2-substituted chromans of high enantiomeric purity is described. Mitsunobu reaction of homochiral halopropanols 10 with 2-bromophenol (9), followed by treatment with n-butyllithium under Parham cycloalkylation conditions generates 2-substituted chromans 7. The methodology was applied to the synthesis of the natural product tephrowatsin E (5) and the antiviral BW683C (6).