α,α-二乙酰基二苄硫缩烯酮的碱催化脱乙酰基反应及缩合反应机理研究

α-羰基二硫缩烯酮是一类极其重要的有机合成中间体，烷硫基对该类具有推-拉电子效应的共轭体系的性质影响很大。据此，我们率先提出了烷硫基对α-羰基二硫缩烯酮类化合物的化学行为具有调控作用的观点，并将其归因于空间电子因素的作用，α-乙酰基-α′-羰基二苄硫缩烯酮(1)具有多反应性特征。近来，我们利用该特征在氢氧化钠催化下通过化合物1的环合合成了多取代噻吩类化合物；在乙醇钠-醋酸铅作用下经乙氧基对化合物1的苄硫基的取代实现了α-羰基-O，O-缩烯酮的合成。

Studies on the Mechanism of Deacylation and Condensation Reactions of α,α-Diacetyl Ketene Dibenzylthioacetal

The behavior of α,α-diacetyl ketene dibenzylthioacetal 1a under basic conditions was studied. Catalyzed by steric hindered base ast-BuONa(int-BuOH), α-acetyl ketene dibenzylthioacetal 2a could be obtained in 98% yield within 3 min via deacylation of 1a. Assisted byt-BuONa(int-BuOH), α-cinnamoyl ketene dibenzylthioacetals were produced in high yields by reacting both 1a and 2a with arylaldehydes; whereas, under the same conditions, the corresponding α,α-dicinnamoyl ketene dibenzylthioacetals 4 were formed when furan-2-carbaldehyde and thiophene-2-carbaldehyde were used asthe electrophiles. These evidences support the proposed mechanism that, catalyzed byt-BuONa (int-BuOH), the reaction of 1a with arylaldehydes may normally proceed via a sequential deacylation-condensation process and the formation of double condensation products 4 may be due to the higher activity of furan-2-carbaldehyde and thiophene-2-carbaldehyde under the selected reaction conditions.