Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Reaction of Di(tert-butyl)- and Diphenyldiazomethane and 1,3-Thiazole-5(4H)-thiones: Isolation and Crystal Structure of the Primary CycloadductReactions of diazo compounds with C=S bonds proceed via the formation of thiocarbonyl ylides, which, under the reaction conditions, undergo either 1,3-dipolar cycloadditions or electrocyclic ring closer to thiiranes (Scheme 1). With the sterically hindered di(tert-butyl)diazomethane (2c), 1,3-thiazole-5(4H)-thiones 1 react to give spirocyclic 2,5-dihydro-1,3,4-thiadiazoles 3 (Scheme 2). These adducts are stable in solution at -20°, and they could be isolated in crystalline form. The structure of 3c was established by X-ray crystallography. In CDCl3 solution at room temperature, a cycloreversion occurs, and the adducts of type 3 are in an equilibrium with 1 and 2c. In contrast, the reaction of 1 with diphenyldiazomethane (2d) gave spirocyclic thiiranes 4 as the only product in high yield (Scheme 3). The crystal structure of 4b was also determined by X-ray analysis. The desulfurization of compounds 4 to 4,5-dihydro-5-(diphenylmethylidene)-1,3-thiazoles 5 was achieved by treating 4 with triphenylphosphine in boiling THF. The crystal structure of 5f is shown.
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