Synthesis of Sulfur-Containing Exo-Bicyclic Dienes and Their Diels–Alder Reactions To Access Thiacycle-Fused Polycyclic Systems

摘要

The stereocontrolled synthesis of unprecedented sulfur-containing exo -bicyclic 1,3-dienes is reported through a palladium-catalyzed reductive cyclization of sulfur-linked 2-bromoenynes. The fused bicyclic structure provides a better stability to the thiacyclic diene compared to the simple 3,4-dimethylenetetrahydrothiophene. Their reactivity toward several dienophiles has been investigated, and various original thiacycle-fused polycyclic systems have been obtained with high or total diastereoselectivity. Moreover, they are the first exo -bicyclic dienes used in Diels–Alder reactions. The relative configurations of four cycloadducts have been unambiguously assigned by X-ray crystallographic analysis. Mechanistic details of the cycloadditions have been examined by computational means.