Carbodiimides react effectively with β-aryl/alkyl-β-hydroxy-α,α-difluorocarboxylic acids to afford a vast array of fully substituted gem-difluorodihydrouracils through a two step reaction sequence. In the first step, condensation between the two reactants leads in most cases to the formation of a mixture of the desired dihydrouracils and N-acylurea co-products. However, the latter could be easily recovered and efficiently converted into the target compounds. The sequence works well in very mild conditions (CH2Cl2, 20 ËC) and the reaction resulted to be completely regioselective when asymmetric carbodiimides were used. When the N-acylurea derivatives are not sufficiently stable for isolation, the process could be done in a one-pot fashion leading to the direct formation of the desired dihydrouracils, although in lower yields.
An effective synthesis of 2,2-difluoro-3-hydroxy esters
作者:Yanchang Shen、Ming Qi
DOI:10.1016/0022-1139(93)02961-d
日期:1994.6
Reformatsky reactions of bromodifluoroacetate with carbonyl compounds and its applications to the synthesis of 2,2-difluoro-3-hydroxy esters as a means of two-carbon homologation with a difluoro moiety under mild conditions in good to excellent yields are described. In the case of aldehydes and aromatic ketones no catalyst was needed, while in the case of aliphatic ketones, 2 mol% of CeCl3 catalyst raises the yields dramatically from 30%-32% to 89%-92%.
The Mitsunobu reaction in the synthesis of α,α-difluoro-β-amino acids
作者:Natalie A. Fokina、Andrei M. Kornilov、Valery P. Kukhar
DOI:10.1016/s0022-1139(01)00430-4
日期:2001.9
A three-stage strategy is proposed to prepare alpha,alpha -difluoro-beta -amino acids starting from aldehydes and with ethyl bromodifluoroacetate as a fluorine source. The Mitsunobu reaction as a key step was studied by P-31 and F-19 NMR for alkyl- and aryl-substituted alpha,alpha -difluoro-beta -hydroxyesters and performed under optimized conditions giving the target compounds. (C) 2001 Elsevier Science B.V. All rights reserved.
Palladium-catalyzed Heck-type reaction of secondary trifluoromethylated alkyl bromides
作者:Tao Fan、Wei-Dong Meng、Xingang Zhang
DOI:10.3762/bjoc.13.258
日期:——
palladium-catalyzed Heck-type reaction of secondary trifluoromethylated alkylbromides has been developed. The reaction proceeds under mild reaction conditions with high efficiency and excellent functional group tolerance, even towards formyl and hydroxy groups. Preliminary mechanistic studies reveal that a secondary trifluoromethylated alkyl radical is involved in the reaction.