Furo[2,3-c]pyrans from a vinyl sulfone modified methyl 2,6-o-anhydro- α- d -hexopyranoside: An experimental and theoretical investigation

A vinyl sulfone modified bicyclic sugar molecule undergoes efficient Michael addition of hetero- and carbon nucleophiles to afford single diastereomers. The same molecule consisting of two other masked functional groups, namely an aldehyde and an oxocarbonium ion, turned out to be a unique synthetic intermediate. The adducts generated from this Michael acceptor and a series of β-dicarbonyl compounds and related reagents after acid treatment afforded a new class of furo[2,3-c]pyrans, forming up to three new bonds and three stereocenters. In-built chirality centers of the sugar derivative controlled the diastereoselectivity of formation of all new bonds without the requirement for any external reagent for asymmetric induction. DFT calculations revealed the formation of furopyrans as the only possible products, which corroborates the experimentally observed results. A vinyl sulfone modified methyl 2,6-O-anhydro-α-D-hexopyranoside has been synthesized for the first time. The β-dicarbonyl adducts of this Michael acceptor, under acidic conditions, yielded furo[2,3-c]pyrans. Computational studies rationalized the experimentally observed results.