Fluorinated β-Diketones in Reactions with Diazocyclopropane Generated in situ

Treatment of 1,1‐di‐ and 1,1,1‐trifluoroalkane‐2,4‐diones 10−13 with cyclopropyldiazonium intermediates 2 and 3, generated in situ through the decomposition of N‐cyclopropyl‐N‐nitrosourea 1 by treatment with moist K2CO3, did not result in the expected azo coupling of the cyclopropyldiazonium ion, but afforded the corresponding oxaspiropentanes 14−17 as products of the addition of diazocyclopropane (3) onto one of the carbonyl groups. In addition, the reaction proceeded selectively on the carbonyl groups adjacent to the di‐ or trifluoromethyl substituents. 1,1‐Difluoroacetone reacted analogously with diazocyclopropane (3) generated in situ, giving stable 2‐(difluoromethyl)‐2‐methyloxaspiropentane in approximately 50% yield. The resulting oxaspiropentanes 14−17, on heating or in the presence of lithium iodide, rearranged selectively into cyclobutanones 20−23, while in the presence of Al2O3 they formed mixtures of approximately equal amounts of the corresponding cyclobutanones and the 1‐vinylcyclopropanols 24−27. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)