Phosphine Sequentially Catalyzed Domino 1,6-Addition/Annulation: Access to Functionalized Chromans and Tetrahydroquinolines with an Ethynyl-Substituted All-Carbon Quaternary Center.

A novel phosphine sequentially catalyzed domino 1, 6-addition/annulation process has been developed using p-quinone methides ( p-QMs) and α-substituted allenoates which generates a series of chroman and tetrahydroquinoline derivatives containing an ethynyl-substituted all-carbon quaternary center with up to 97% yield and 20:1 dr. value. In this reaction, allenoates act as C2 synthons.