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 K 2 CO 3 , 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 Al 2 O 3 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)