Quaternary and Tertiary Carbon Centers Synthesized via Gallium-Catalyzed Direct Substitution of Unfunctionalized Propargylic Alcohols with Boronic Acids.

(IPr)GaCl3/AgSbF6, AgSbF6, and GaCl3 catalyzed substitution of the hydroxyl of secondary and tertiary propargylic alcohols with organoboronic acids via C-C bond formation, and GaCl3 effectively synthesized all-carbon quaternary propargylic centers. These catalysts performed the substitution at carbons bearing alkyl substituents, which has been problematic for other systems. Highly hindered carbon stereocenters were thus produced, including quaternary centers bearing doubly ortho-substituted aryl rings, that are difficult to access with traditional methods.