Synthesis of a Diacetonide-Protected, Mannose-Based Oxepine: Configurational Control of Anomeric Acetate Activation.

Carbohydrate-based oxepines are seven-membered-ring oxacycles containing an enol ether moiety. These compounds have been used as intermediates in the preparation of septanose carbohydrates by functionalization through their double bond. Reported here is a new synthesis of a carbohydrate based oxepine that uses 2,3;4,6-di- O -acetonide mannose as a key starting material. The oxepine is an important precursor used in the synthesis of septanose glycomimetics of mannopyranosides. The central feature of the synthesis is a two-step sequence that converts a septanose 1,2-di- O -acetate to the septanosyl bromide and onward to the oxepine via a reductive elimination.