[2+3] Cycloadditions of ‘Thiocarbonyl Ylides’ (= (Alkylidenesulfonio)methanides) and diazoalkanes with N,N′‐(thiocarbonyl)diimidazole (= 1,1′‐(carbonothioyl)bis[1H‐imidazole])

Abstract

Heating of a mixture of N,N′‐(thiocarbonyl)diimidazole (= 1,1′‐(carbonothioyl)bis[1H‐imidazole]; 1) and 2,5‐dihydro‐1,3,4‐thiadiazole 2a or 2b gave the 1,3‐dithiolanes 4a and 4b, respectively, via a regiospecific 1,3‐dipolar cycloaddition of the corresponding ‘thiocarbonyl methanides’ 3a,b onto the CS group of 1 (Schemes 1 and 2). The adamantane derivative 4b was not stable in the presence of 1H‐imidazole and during chromatographic workup. The isolated 1,3‐dithiole 5 is the product of a base‐catalyzed elimination of 1H‐imidazole from the initial cycloadduct 4b. The formation of the S,N‐acetal 6 can be rationalized by a protonation of the ‘thiocarbonyl ylide’ 3b followed by a nucleophilic addition of 1H‐imidazole. With the diazo compounds 8a–e (Scheme 3) 1 underwent a regiospecific 1,3‐dipolar cycloaddition to give the corresponding 2,5‐dihydro‐1,3,4‐thiadiazole derivatives 9, which spontaneously eliminated 1H‐imidazole to yield (1H‐imidazol‐1‐yl)‐1,3,4‐thiadiazoles 10. The structures of 10a and 10d were established by X‐ray crystallography. In the case of diazodiphenylmethane (8f), the initial cycloadduct 9f decomposed via a ‘twofold extrusion’ of N2 and S to give 1,1′‐(2,2‐diphenylethenylidene)bis[1H‐imidazole] (11; Scheme 3).

Synthesis of aromatic heterocycles

“…184 Ethyl diazoacetate and other diazo compounds react with thiocarbonylbis(imidazole) to give 1,3,4-thiadiazoles by 1,3-dipolar addition to the C᎐ ᎐ S bond, and not 1,2,3-thiadiazoles as was reported earlier. 185 11 Triazoles, benzotriazoles and tetrazoles 1,2,3-Triazole has been isolated in up to 75% yield from the reaction of dichloroacetaldehyde tosylhydrazone with ammonia (Scheme 52). When primary amines are used in place of ammonia, 1-substituted triazoles are formed in good yield.…”

1,1′-Thiocarbonyldiimidazole

“…Lewis acid catalysis, however, induces rearrangement leading to the thiadiazoles with the O and S transposed (eq 23). Thiocarbonyl ylides, obtained upon heating 2,5-dihydro-1,3,4-thiazoles, add to TCDI to form dithiolanes (eq 24) 72. Finally, TCDI, or its immediate derivatives, have been used in a variety of pericyclic processes.…”