gem-difluorinated 2H-furans from reactions of BrCF2CO2Et with enaminones has been described. The reactions tolerate a wide variety of functional groups under metal-free conditions. An active aminocyclopropane is proposed to be a key intermediate through the cyclopropanation of difluorocarbene with enaminones, which further triggers a regioselective C–C bond cleavage in situ to afford the corresponding gem-difluorinated
已经描述了由 BrCF 2 CO 2 Et 与烯胺酮反应合成偕二氟化 2 H-呋喃的级联策略。该反应在无金属条件下耐受多种官能团。通过二氟卡宾与烯胺酮的环丙烷化反应,活性氨基环丙烷被认为是关键中间体,这进一步引发了区域选择性 C-C 键原位断裂,得到相应的偕二氟化2 H-呋喃。
Highly Selective Rhodium-Catalyzed Conjugate Addition Reactions of 4-Oxobutenamides
作者:Jamie L. Zigterman、Jacqueline C. S. Woo、Shawn D. Walker、Jason S. Tedrow、Christopher J. Borths、Emilio E. Bunel、Margaret M. Faul
DOI:10.1021/jo701682c
日期:2007.11.1
[GRAPHICS]A variety of 4-oxobutenamides 1 were subjected to rhodium-catalyzed conjugate addition with arylboronic acids providing high regio- and enantioselectivity (97:3 to > 99:1, > 96% ee) and moderate to excellent yields (54-99%). The key to high selectivity is the use of sterically demanding P-chiral diphosphines, such as Tangphos or Duanphos. The product oxobutanamides 2 may be converted to alternate targets by selective derivatization of either the amide or ketone functional group. A stereochemical model predicting the absolute sense of induction was developed based on single-crystal X-ray structures of product and precatalyst.