Abstract
The reactions of aryl (selenophen-2-yl) thioketones with CH2N2 occur with spontaneous elimination of N2, even at low temperature (-65°), to give regioselectively sterically crowded 4,4,5,5-tetrasubstituted 1,3-dithiolanes and/or a novel type of twelve-membered dithia-diselena heterocycles as dimers of the transient thiocarbonyl S-methanides. The ratio of these products depends on the type of substituent located at C(4) of the phenyl ring. Whereas the formation of the 1,3-dithiolanes corresponds to a [3 + 2] cycloaddition of an intermediate thiocarbonyl ylide with the starting thioketone, the twelve-memberd ring has to be formed via dimerization of the 'thiocarbonyl ylide' with an extended biradical structure.
Mlostoń, Grzegorz