Dearomative indole [5+2] cycloaddition reactions: stereoselective synthesis of highly functionalized cyclohepta[b]indoles.

The first dearomative indole [5+2] cycloaddition reaction with an oxidopyrylium ylide resulted in efficient and diastereoselective construction of some highly functionalized and synthetically challenging oxacyclohepta[b]indoles. The protocol proceeds under very mild reaction conditions, thus enabling high functional-group tolerance and unique endo selectivity.