Pd-catalyzed cross-coupling of aryl carboxylic acids with propiophenones through a combination of decarboxylation and dehydrogenation

摘要

A palladium-catalyzed cross-coupling reaction of aryl carboxylic acids with saturated propiophenones through a combination of decarboxylation and dehydrogenation to form Heck-type products was reported. In a glove box, a 25 mL tube equipped with a stir bar was charged with Pd(OAc) _2, PCy _3, propiophenone, 2-nitrobenzoic acid, Ag _2CO _3 and nBu _4NOAc HOAc. Then, the mixture was heated under nitrogen at 90°C in DMF for 24 h. After cooling down, the crude reaction mixture was analyzed by GC with n-dodecane as an internal standard to obtain 3a in 75 GC yield. Relatively weak bases, such as carboxylate salts, facilitated this reaction and the effect of the bases was a function of their solubility, while strong bases, such as K _3PO _4 and K _2CO _3 shut down the reaction completely. The simultaneous use of carboxylate salts and equimolar carboxylic acids significantly improved the yield of 3a, although the use of acetic acid alone was ineffective for the reaction.