Highly Chemoselective Methylation and Esterification Reactions with Dimethyl Carbonate in the Presence of NaY Faujasite. The Case of Mercaptophenols, Mercaptobenzoic Acids, and Carboxylic Acids Bearing OH Substituents
作者:Maurizio Selva、Pietro Tundo
DOI:10.1021/jo0520792
日期:2006.2.1
with several ambident nucleophiles such as o- and p-mercaptophenols (1a,b), o- and p-mercaptobenzoic acids (2a,b), o- and p-hydroxybenzoic acids (3a,b), mandelic and phenyllactic acids (4, 5), have been explored under batch conditions. Highly chemoselective reactions can be performed: at 150 °C, compounds 1 and 2 undergo only a S-methylation reaction, without affecting OH and CO2H groups; at 165 °C,
在的NaY的存在八面沸石,碳酸二甲酯(DMC)的与若干两可的亲核试剂,如反应ø -和p -mercaptophenols(1A ,b),邻-和p -mercaptobenzoic酸(图2a ,b),邻-和p -羟基酸(图3a ,b),扁桃和phenyllactic酸(4,5),已被分批条件下探索。可以进行高度化学选择性的反应:在150°C下,化合物1和2仅进行S-甲基化反应,而不影响OH和CO 2 H基团;在165℃下,酸3 - 5形式相应的甲基酯,同时兼具它们的芳族和脂族OH的取代基是完全由甲基化和/或酯交换方法保存。典型的选择性为90-98%,产品(分别为S-甲基衍生物和甲酯)的分离产率为85-96%。还报道了使用K 2 CO 3作为催化剂的比较研究。尽管事实证明,碱(K 2 CO 3)比沸石更具活性,但化学选择性却难以捉摸:化合物2a ,b同时经历S-甲基化反应和酯化反应,和酸3 -