Fused thiazolidine 11 and thiazoline derivatives Ha-c are obtained by intramolecular cycloaddition-elimination reactions of appropriately substituted Mninothiatriazolines 10 and Ha-c. The incorporation of a sidechain phenyl group excercises a favorable effect on cycllxation since no reaction is observed with 25. Comparable intermolecular reactions also fail to occur. Recently we reported that 5-(cyan0 tethered)imino-A*-1,2,3,Cthiatriaxolines 1 thermolyze with loss of nitrogen to give fused 1,2,4-thiadiazole derivatives 3.' These intramolecular cycloaddition-elimination reactions are assumed to proceed via thiapentalenoid intermediites 2 having a tetravalent sulfur atom.* In continuation of this research we have now extended this reaction principle to 5-imino-1,2,3,4-thiatriaxolines bearing an oletin or acetylene group at the imine function. The results are discussed below.
A convenient method for the synthesis of the functionalized thiatriaxoline 10 starts from o-tolualdehyde 4 and proceeds through a series of transformations outIiied in Scheme 1. Thus, the Wittig-Homer olefination of 4 with diethyl ethoxycarbonylmethylphosphonate in a two-phase liquid-solid system) furnished ethyl cinnamate 5 in high yield. This compound was brominated with N-bromosuccinimide following a known procedure4 and then converted into the thiatriaxole 9 by a classical method.5
Methylation of 9 was performed with Meerwein's reagent and produced exclusively the N-4 methylated product 1O.6 This compound was fully characterized by spectral methods (IR, 'H NMR and "C NMR)