Synthesis of Five-Membered Sulfur-Heterocycles via 1,5-Dipolar Electrocyclization of Thiocarbonyl Ylides and Related Processes

The reactive thiocarbonyl ylides belong to the less well-known class of the so-called ‘sulfur-centered 1,3-dipoles’. Only in recent years have the [2+3] cycloadditions with thiocarbonyl ylides been extensively explored, mainly as a useful method for the synthesis of three- and five-membered sulfur heterocycles. The goal of the present review is to demonstrate the potential of the 1,5-dipolar electrocyclization of properly substituted thiocarbonyl ylides as an alternative approach to syntheses of sulfur heterocycles such as 1,3- oxathiolanes, 1,3-thiazoles, 1,3-dithioles, and thiophenes. Thermal, as well as metal-catalyzed, generations of the reactive intermediates from diazo and thiocarbonyl precursors are summarized and discussed. The presented examples show the scope and limitations of this general but relatively scarcely-investigated reaction.