Synthesis of Sugar Diene and Its Pd-Catalyzed Transformation into Chromanes

A route to synthesize 1,2-disubstituted glucals has been developed, which were further converted to substituted chromanes by thermal 6π-electrocyclization in HMPA followed by in situ aromatization. One of the key steps in the synthesis of chromane is metal-free generation of C1-substituted glucal from d-mannose, which was further converted to 1,2-disubstituted glucals by Pd-catalyzed Fujiwara-Moritani reaction with styrenes, acrylates, acrylamide, acrylonitrile, and ethyl vinyl ketone in good yields.