The Friedel-Crafts reactions of 2,2-difluorocyclopropanecarbonyl chloride with various arenes did not lead to the straightforward formation of the expected aryl 2,2-difluorocyclopropyl ketones. Instead the reactions proceeded, to various degrees depending on the reactivity of the arene, via an apparent rearrangement of the initially formed acylium ion to form novel aryl 3-chloro-3,3-difluoropropyl ketones. The ring-opened product was formed exclusively, and therefore the reaction may be synthetically useful when relatively unreactive arene substrates such as benzene, toluene, and p-xylene are used. No conditions were found where ring-intact products could be formed exclusively when using substituted benzenes as substrates, with the very reactive substrate thiophene being most selective in that regard, favoring ring intact product 3 with a selectivity of 98:2. The regioselectivity of ring-opening was examined and compared with other related systems computationally.

Friedel-Crafts Reactions of 2,2-Difluorocyclopropanecarbonyl Chloride: Unexpected Ring-Opening Chemistry. -AlCl3-mediated treatment of the title chloride (I) with arenes results in formation of aryl cyclopropyl ketones and/or unexpected ring--opening products of type (II). Their ratio is dependent on the reactivity of arenes and conditions used. -(DOLBIER*, W. R. J.; CORNETT, E.; MARTINEZ, H.; XU, W.; J. Org. Chem. 76 (2011) 9, 3450-3456, http://dx.