Synthesis of Seven-Membered Ring Nucleosides and Serendipitous Simmons-Smith O -Glycosylation.

A series of seven-membered (oxepine) nucleosides containing various nucleobases (A, U, T, 5-FU, C) were synthesized by ring expansion of cyclopropanated glucals. We expect this new series of ring-expanded nucleic acid analogues to be useful as building blocks in the design of mixed base functional genetic systems. While exploring alternative pathways to oxepine nucleoside synthesis, we discovered an unprecedented α-stereoselective O -glycosylation of 1,2-glucals under mild Simmons-Smith conditions.