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Reaction of Mesoionic Thiazol-4-ones with Azodicarbonyl Dipolarophiles. Cleavage Modes of the Bi- and Tri-cyclic Adducts
Sheradsky, Tuvia,Itzhak, Norbert
, p. 1979 - 1986 (2007/10/02)
The thiazolium-4-olates (1a-e) were treated with dimethyl and diethyl azodicarboxylate and gave, through 1,3-dipolar cycloaddition, the 3,6-sulphur bridged hexahydro-1,2,4-triazin-5-ones (2).When heated in benzene these rearranged to the blue thioxohydrazides (3), whilst when heated in methanol or ethanol they reacted with the solvent to give 2-alkoxy-5-hydrazinothiazol-4-ones (4).Reaction of the mesoionic compounds (1) with 4-phenyl-1,2,4-triazole-3,5-dione (PTAD) gave the cycloadducts (11) which reacted very readily with water or alcohols to give the thiazol-4-ones (5), analogous to (4).The structures and stereochemistry of (2), (3), and (5) were established by X-ray analyses.The mechanisms of the ring openings of (2) to (3) and (4), and of (11) to (5) are discussed.
