Gold-catalyzed homo- and cross-annulation of alkynyl carboxylic acids: a facile access to substituted 4-hydroxy 2H-pyrones and total synthesis of pseudopyronine A.

A Au(i)-catalyzed homo- and cross-annulation reaction of alkynyl carboxylic acids offering 3,6-disubstituted 4-hydroxy 2H-pyrones has been demonstrated. The reaction tolerates various substituted alkynyl carboxylic acids and moderate to good yields of α-pyrone scaffolds have been observed. Later, a gram-scale reaction of the acid and the total synthesis of the natural product pseudopyronine A have been carried out successfully.