The acid catalyzed cyclization of diazoketones: Preparation of 2,4(3H,5H) furandiones

Diazoketones derived from substituted ethyl hydrogen malonates produced by the selective hydrolysis of the corresponding malonate esters cyclize in the presence of catalytic amounts of boron trifluoride etherate in methanol to yield 2,4(3H,5H) furandiones. The cyclic keto orthoesters appear to be intermediates in the reaction. © 1987.