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.