Cyclization reactions using vinyl sulfides and vinyl selenides: Recent developments towards organic synthesis

Cyclization reactions using vinyl sulfides and vinyl selenides have recently attracted much attention. One of the major characteristics of sulfur-and selenium-substituted donor olefins is a large HOMO coefficient on the hetero-atom. Due to such specific character, sulfur and selenium-substituents can be used as selectivity-controlling elements in cyclizations. Novel reactions resulting from a combination with other elements, such as [2+1] cycloadditions of 1-seleno-2-silylethenes, are also described. After the cyclization steps, sulfur and selenium are useful for various functional group transformations. In this review, [2+1], [2+2], [3+2], and [4+2] cycloaddition reactions employing vinyl sulfides and selenides in organic synthesis are outlined.