Total Syntheses of Avapyran and Dysiquinol D through a Stereoconvergent Fusion of Dihydrobenzopyran.

Asymmetric total syntheses of avapyran, dysiquinol D, and 8-epi-dysiquinol D are reported. The key steps involved in the syntheses are selective formation of an all-carbon quaternary stereocenter under Birch conditions, an unprecedented acid-mediated stereoconvergent installation of a cis-dihydrobenzopyran unit, and the reagent-controlled regioselective dehydration of tertiary alcohol.