二氧化碳: 一种同时提供亲核中心保护和亲电中心活化的试剂 XI:2-取代四氢噻唑的新合成方法

四氢噻唑和正丁基锂反应生成的N-锂代四氢噻唑(2)与二氧化碳作用生成N-羟酸锂盐3; 3然后在叔丁基锂作用下失去2-位质子形成相应的2-位碳阴离子4; 该碳阴离子和一系列亲电试剂反应, 并在酸性条件下除去保护基团得产物-2-取代四氢噻唑7. 在此过程中, 二氧化碳既是氨基的保护基团, 同时又活化了2-位亲电中心.此方法不需分离各步中间体, 产率中等.

Carbon dioxide: A reagent for the simutaneous protection of nucleophilic centers and the activation of alternative locations to electrophilic attack XI:A new synthetic route to the 2-substituted thiazolidines

Thiazolidine is readily converted into 2-substituted derivatives I [R = D, Me, Et, Bu, hexyl, octyl, CH2Ph, CO2H, CPh2OH, CH(OH)C6H4Me-4] in a 1-pot lithiation procedure, with CO2 as both an N protection agent and as an intermediate carbanion-stabilizing group. The procedure has 4 stages: (1) protection of the NH group by lithiation and subsequent treatment with CO2 to form the Li carbamate; (2) lithiation by Me3CLi to form the carbanion; (3) introduction of a substituent by reaction with an electrophile; (4) acidic removal of the N protecting group. The yields of the products are mostly moderate.