2,3-Dihydro-1,4-dithiins and the isomeric 2-alkylidene-1,4-dithianes were synthesized from 1,2-diketones and alkyl pyruvates by kinetically controlled ring expansion of 2-(1-hydroxyalkyl)-1,3-dithiolanes with p-toluenesulfonyl chloride in pyridine. In addition, 2,3-dihydro-1,4-dithiins, the thermodynamic products, were formed exclusively by using p-toluenesulfonic acid in refluxing benzene. The 2-alkylidene-1,4-dithianes were readily isomerised to the corresponding 2,3-dihydro-1,4-dithiins. Similarly, 2,3-dimethyl-6, 7-dihydro-5H-1,4-dithiepine and (+)-2-methylene-3-methyl-1,4-dithiepane were obtained from 2-[(S)-1-hydroxyethyl]-2-methyl-1,3-dithiane.
2,3-二氢-1,4-二
硫烯和异构的2-烷基烯-1,4-二
硫烷是通过在
吡啶中用
对甲苯磺酰氯对2-(1-羟基烷基)-1,3-二
硫烷进行动力学控制的环扩展,从1,2-二酮和烷基
丙酮酸酯合成的。此外,使用
对甲苯磺酸在回流苯中,可以专门形成热力学产物2,3-二氢-1,4-二
硫烯。2-烷基烯-1,4-二
硫烷可轻易异构化为相应的2,3-二氢-1,4-二
硫烯。同样,2,3-二甲基-6,7-二氢-5H-1,4-二
硫哌啶和(+)-2-亚甲基-3-甲基-1,4-二
硫烷是由2-[(S)-1-羟基乙基]-2-甲基-1,3-二
硫烷得到的。