Cycloaddition of homophthalic anhydrides with aldehydes and ketones: a route to 3,4-dihydroisocoumarin-4-carboxylic acid derivatives

Homophthalic anhydride reacts with benzaldehyde in the presence of boron trifluoride-diethyl ether complex to give the cycloadduct 3-phenyl-3,4-dihydroisocoumarin-4-carboxylic acid in good to excellent yield. Under these conditions we did not observe the formation of Perkin-type products. The reaction can be extended to a wide variety of aldehydes and to some ketones in synthetically useful yields. Amides can be obtained in good yields after activation of the carboxylic function with DCC at O°C.