碳水化合物衍生的手性配体——25含碳水化合物单元的膦配体在钯催化的Heck反应中的应用

Chiral Ligands Derived from Carbohydrate——25 Application of a Phosphine with Carbohydrate Unit in the Palladium-Catalyzed Heck Reaction

评价了一种碳水化合物衍生的具有较大立体位阻及较三苯基膦更富电子的膦配体(甲基3-脱氧-3-二苯膦基-4,6-氧-苯次甲基-α-D-吡喃阿卓糖苷,3-MBPA)在Pd催化的Heck反应中的性能.发现在N,N-二甲基乙酰胺溶剂中K2CO3是该催化体系较适合的碱;在该配体的支持下催化剂中钯的用量可低至0.5 mo1%;可催化苯乙烯与带给电子基团的溴代芳烃及带吸电子基团的氯代芳烃发生反应,高产率地生成相应的偶联产物;反应区域选择性表明,Pd(OAc)2/3-MBPA体系在催化苯乙烯与卤代芳烃的Heck反应中并存阳离子催化途径,说明3-MBPA中的氧原子可能也参与配位;同时发现,加入助配体四丁基溴化胺(TBAB)后,可能是Br-参与配位有利于增加中性催化途径的机会而提高了反应区域选择性.

A phosphine（methyl 3-deoxy-3-diphenylphosphino-4,6-O-phenylmethenyl-α-D-altropyra-noside,3-MBPA） derived from carbohydrate,which is steric demanding and richer on electron than triphenylphosphine,has been evaluated as supporting ligand in the palladium-catalyzed Heck reaction.It is found that K2CO3 is suitable as base for the catalyst system Pd（OAc）2/3-MBPA in N,N-dimethyl ace-tylamine,and excellent yields have been achieved by the loading of palladium source down to 0.5 mol% for styrene coupling with aryl bromides containing electron-donating substituent and aryl chlorides containing electron-withdrawing substituent.The regioselectivities of the arylation of styrene catalyzed by the system indicate that the ion path co-exists in the coordination-insertion step,although the neutral path is favorite,meaning that the oxygen atoms of 3-MBPA coordinate to palladium probably.Besides,the regioselectivities raise through the coordination of Br-to palladium center to favour the neutral path by adding TBAB.