TRIBUTYLSTANNANE-MEDIATED CYCLIZATION OF THIONOCARBOXYLIC ACID-DERIVATIVES

Cyclization reactions of various thionoesters and thioamides involving the addition of tri-n-butylstannyl radical to a thiocarbonyl group and intramolecular addition of the resulting radical to a carbon-carbon multiple bond was studied. Dithiocarbonate and (imidazolyl)thiocarbonyl derivatives of homoallylic alcohols gave alpha-substituted gamma-thionobutyrolactones. The reaction is highly dependent on the substitution pattern on the double bond, a high yield of cyclic products being obtained only when the double bond is activated and unhindered. (Z)-4-Phenylbut-3-enyl thionobenzoate afforded 4,5-dihydro-2-phenyl-3-benzylfuran in low yield. In reactions involving a thioamide group, good yields of cyclic products were obtained only from compounds in which the electron density on the nitrogen atom is decreased by an electron attracting group. Cyclization of 1-((E)-4-phenylbut-3-en-1-yl)-5-thioxopyrrolidin-2-one (23) afforded 1-aza-4-benzylbicyclo[3.3.0]oct-4-en-8-one (33).