Rh-Catalyzed Coupling of Acrylic/Benzoic Acids with α-Diazocarbonyl Compounds: An Alternative Route for α-Pyrones and Isocoumarins.

A coupling of acrylic acids/benzoic acids with α-diazocarbonyl compounds has been realized by a combined catalytic system of rhodium catalyst and Zn(OAc) additive. The presence of Zn(OAc) obviously accelerates the C(sp)-H activation and destructed the formation of carboxylic ester that is formed via a nucleophilic O-H insertion to metal carbenoid. The procedure featured mild reaction conditions and broad substrate scope, providing a straightforward approach to the synthesis of α-pyrones and isocoumarins without the transformation of carboxylic acids to the corresponding amides.