Ketenimines as intermediates in the hydrolytic decyanation of alpha-cyano-gamma-lactones

alpha-Cyano-gamma-lactones underwent replacement of the cyano group by H to yield the corresponding gamma-lactones when treated with wet alumina in a variety of solvents. The mechanism of this new hydrolytic decyanation is di scussed in terms of the initial formation of tautomeric ketenimines which r eact with water to form ketenes, which in turn undergo further hydration to give carboxylic acids that subsequently decarboxylate to yield gamma-lacto nes. The proposed hydration reactions are consistent with two successive pl anar [4 + 2] pseudopericyclic transition structures. This operationally sim ple procedure affords novel 2-oxofuro[2,3-b]indoles in good yields.