Wu Qiuyue, Yang Zhanhui, Xu Jiaxi
State Key Laboratory of Chemical Resource Engineering, Department of Organic Chemistry, Faculty of Science, Beijing University of Chemical Technology, Beijing 100029, P. R. China.
Org Biomol Chem. 2016 Jul 26;14(30):7258-67. doi: 10.1039/c6ob01259k.
The annuloselectivity in the reactions of methanesulfonyl sulfene and imines varies with temperature. At a relatively higher temperature of 20 °C, the [2(s) + 2(i)] annulation of different N-alkyl imines occurs exclusively, giving four-membered trans-β-sultams in up to 69% yields. At a lower temperature of -78 °C, the [2(s) + 2(i) + 2(i)] annulation of N-methyl imines takes place specifically, delivering six-membered 1,2,4-thiadiazine 1,1-dioxides, 4-aza-δ-sultams, in up to 80% yields, with diverse configurations at the C3, C5, and C6 stereocenters. The trans-stereochemistry involved in the [2(s) + 2(i)] annulations is attributed to the conrotatory ring closure of the thermodynamically stable 2,3-thiazabutadiene-type zwitterionic intermediates, while the diverse stereochemical outcomes in the [2(s) + 2(i) + 2(i)] annulations are caused by the iminium isomerization in the stepwise nucleophilic [4 + 2] annulation between the same zwitterionic intermediates and a second molecule of N-methyl imines.
甲磺酰基亚磺烯与亚胺反应中的环化选择性随温度变化。在相对较高的20°C温度下，不同N-烷基亚胺的[2(s)+2(i)]环化反应专一发生，生成产率高达69%的四元反式-β-磺内酰胺。在较低的-78°C温度下，N-甲基亚胺的[2(s)+2(i)+2(i)]环化反应特异性发生，生成产率高达80%的六元1,2,4-噻二嗪1,1-二氧化物、4-氮杂-δ-磺内酰胺，在C3、C5和C6立体中心具有多种构型。[2(s)+2(i)]环化反应中涉及的反式立体化学归因于热力学稳定的2,3-噻唑丁二烯型两性离子中间体的顺旋环化，而[2(s)+2(i)+2(i)]环化反应中多样的立体化学结果是由相同两性离子中间体与第二个N-甲基亚胺分子之间逐步亲核[4+2]环化反应中的亚胺异构化引起的。
