氧化锌促进的醛与Ph3P+CF2H·Br-的Wittig偕二氟烯基化反应

摘要

Wittig gem-difluoroolefination of aldehydes with difluoromethyl phosphonium salt (Ph3P+CF2H·Br-) by using zinc oxide as a base is described.Although the proton in the CF2H group is acidic and a base could easily lead to its deprotonation to form ylide (Ph3P+CF2-),the attack of the base at the positive phosphorus atom may also take place to produce a nucleophilic [HCF2-] equivalent,and then nucleophilic difluoromethylation instead of Wittig reaction would occur.The use of ZnO as the base favored the Wittig reaction and the nucleophilic difluoromethylation was not observed.Furthermore,the excessive ZnO and ZnⅡ salts produced from ZnO could be easily removed by filtration,which may be convenient for the purification process.%以氧化锌为碱实现了醛与二氟甲基鳞盐[Ph3P+CF2H·Br-]的Wittig偕二氟烯基化反应.虽然鳞盐中二氟甲基上的氢原子具有一定酸性,但是碱不一定就会与其发生中和反应而使鳞盐转化为叶立德.碱也有可能进攻磷原子而产生具有亲核性的二氟甲基物种,从而发生亲核二氟甲基化.以氧化锌为碱可抑制二氟甲基化,有利于Wittig反应;此外,氧化锌及其产生的锌盐都可经简单过滤而除去,方便产物纯化.