Tandem Dearomative/Rearomative (3 + 2) Annulation of Aroyl-Substituted Donor-Acceptor Cyclopropanes with Benzothiazoles.

A series of benzo[ d ]pyrrolo[2,1- b ]thiazoles was synthesized by (3 + 2) annulation of aroyl-substituted donor-acceptor cyclopropanes with benzothiazoles. The annulation, promoted by a substoichiometric amount of Sc(OTf) 3 , takes place through the formation of the respective dearomatized (3 + 2) adducts, followed by unexpected decarbethoxylative and dehydrogenative rearomatization to afford fully aromatized products. The unusual reactivity is attributed to the presence of an extra aroyl group in the donor-acceptor cyclopropanes.