Reaction of acceptor-substituted carbonyl compounds with diethylamino sulfur trifluoride

Abstract

The reaction of carbonyl compounds with SF 4 or its derivatives like diethylamine sulfur trifluoride (DAST) is a well-established method for the introduction of fluorine into organic systems. However, in contrast to ‘normal’ aldehydes and ketones (eqn. 1; R and AH, alkyl or aryl), compounds containing an electron-withdrawing group adjacent to the carbonyl group have been used rather infrequently in carbonyl-fluorination. (Reaction with DAST have been described only for few examples.) ▪ R = alkyl, aryl A = CO 2R′, CF 3, CF 2R″ We have found that various acceptor-substituted carbonyl compounds react very easily with DAST (faster than ‘normal’ aldehydes and ketones). This opens up a facile route to α, α-difluoro-substituted carboxylic esters as well as to compounds containing pentafluoroethyl groups or tetrafluoroethylene moieties (eqn. (1). The use of this method is demonstrated in the synthesis of new liquid crystalline materials [ DE Pats 4 002 374 and 4 101600 (Aug. 1, 1991), 4 015 681 (Nov. 21,1991)] to E. Bartmann, E. Poetsch, U. Finkenzeller and B. Rieger (for Merck-Patent GmbH).