PHOTOCYCLOADDITION OF THIOCARBONYL COMPOUNDS TO OLEFINS . REACTION OF THIOBENZOPHENONE WITH VARIOUS TYPES OF OLEFINS

The mechanism of photocycloaddition of thiobenzophenone to various types of olefins has been studied. Electron-rich olefins react with the n,π* triplet state of thiobenzophenone yielding either 1,4-dithiane or thietane derivatives depending on the structure of the olefin. Steric effect is an important factor in determining the reaction path. Electron-deficient olefins react with the π,-π* singlet state of thiobenzophenone giving thietane derivatives. The kinetics and product analyses of the reactions show that the reaction with the former type of olefin proceeds via a radical mechanism, whereas that with the latter type of olefin takes place by a nucleophilic attack of excited thiobenzophenone on the olefins or through complexes between the olefins and the π,π* singlet state of thiobenzophenone. In the reactions that produce 1,4-dithiane derivatives, trans addition of two molecules of thiobenzophenone is verified. The structure and the configuration of the products have been determined both spectro scopically and chemically. © 1969, American Chemical Society. All rights reserved.