Synthesis of Eight-Membered Lactams through Formal [6+2] Cyclization of Siloxy Alkynes and Vinylazetidines
Jianwei Sun and Ian Williams describe the a [6+2] cyclization procedure to synthesize eight-membered lactams.
Medium-sized cyclic compounds are those that typically include an 8- to 11-membered ring (7-membered rings are also sometimes regarded as medium-sized rings) and are wide spread motifs in many kinds of natural products. They are also useful building blocks in the preparation of natural and bioactive compounds. Due to ring strain and trans annular interactions, efficient assembly of these medium-sized compounds has remained a long-standing challenge in organic synthesis. In 2015, the laboratory of Professor Jianwei Sun at the Hong Kong University of Science and Technology (P. R. of China) reported a strategy to synthesize medium-sized lactams from cyclic iminiums and siloxy alkynes in the presence of a Brønsted acid. In collaboration with the laboratory of Professor Ian D. Williams from the same university, they now developed a new approach by further taking advantage of siloxy alkynes and strained rings.