Stereoselective protecting group free synthesis of D,L-gulose ethyl glycoside via multicomponent enyne cross metathesis--hetero Diels-Alder reaction.

An efficient and stereoselective synthesis of D,L-gulose was described. The key step of the synthetic route is represented by a multicomponent enyne cross metathesis-hetero Diels-Alder reaction which allows the formation of the pyran ring from cheap and commercially available substrates in a single synthetic step. The synthesis of D,L-gulose was accomplished without the use of protecting groups making this approach highly desirable also in terms of atom economy.