ABSTRACT
The photochemistry of thiocarbonyl compounds has been extensively studied over the past three decades and many new photochemical reactions have been developed.
Thiocarbonyl compounds, such as thioketones and thioesters, show considerably high photochemical reactivity toward (2+2)-cycloaddition and hydrogen abstraction by thiocarbonyl sulfur. Simple thioamides are generally inert toward photolysis; however, in contrast, cyclic thioamides and arylthioamides show considerable reactivity in a variety of photochemical reactions such as photochemical (2+2)-cycloaddition with various alkenes, and which provides a method for the synthesis of a new C-C bond. The thioimides are more reactive than thioamides toward the photochemical cycloaddition to multiple bonds and hydrogen abstraction by thiocarbonyl sulfur atom. Most thioamides are conveniently prepared by sulfurization of the corresponding amides with thionation reagents such as Lawesson’s reagent or phosphorous pentasulfide. Monothioimides or dithioimides are usually provided by thionation of the corresponding imides with the same thionation reagents or acylation of the corresponding thioamides. The photochemical reaction of thioamides and thioimides provides not only a new photochemical aspect in the area of organic photochemistry but also a useful synthesis of nitrogen-containing heterocycles. Some reviews for thione photochemistry, including thioamides and thioimides, have been reported; therefore, the photochemical reactions in this chapter are limited to those developed in the past ten years.
