Calcium-catalyzed carboarylation of alkynes.

The first transition-metal-free carboarylation of alkynes with commercial and readily available alcohols as alkylating agents was realized in the presence of an environmentally benign calcium catalyst. Thereby, a novel protocol for the one-step synthesis of highly congested, all-carbon tetrasubstituted alkenes, as incorporated in potentially bioactive, complex dihydronaphthalene, chromene and dihydroquinoline structures, is provided. The reaction features an unprecedented, particularly wide substrate scope, good functional-group tolerance and simple experimental operation under mild reaction conditions.