Synthesis of 2H-Chromenes via Unexpected [4 + 2] Annulation of Alkynyl Thioethers with o-Hydroxybenzyl Alcohols.

A novel Brønsted acid-catalyzed reaction of alkynyl thioethers with o-hydroxybenzyl alcohols via an unexpected formal [4 + 2] annulation has been developed. This metal-free protocol leads to the facile and practical synthesis of valuable polysubstituted 2H-chromenes in mostly good to excellent yields under mild reaction conditions and features a wide substrate scope and excellent functional group tolerance.

Synthesis of α,ß-Unsaturated Amidines through Gold-Catalyzed Intermolecular Reaction of Azides with Ynamides.

A concise and flexible synthesis of α,ß-unsaturated amidines via gold-catalyzed intermolecular ynamide amination/carbene 1,2-shift between ynamides and benzylic azides has been developed. Under mild reaction conditions, various α,ß-unsaturated amidines were obtained in mostly good yields, thus providing an efficient and atom-economic way for the construction of valuable α,ß-unsaturated amidines.