Triazoles heterocumulenes

Diazo(trimethylsilyl)methyl lithium (3) was found to be the reagent of choice for the synthesis of azoles from heterocumulenes (Scheme 8.43). The reaction is typically carried out in ether at 0-20 °C. Thus, alkyl- (or aryl-)substituted keteni-mines are transformed into 1,2,3-triazoles 188 (246), while C-acceptor-substituted ketenimines yield either 4-aminopyrazoles 189 or 1,2,3-triazoles, depending on the substituents (247). Isocyanates are converted into 5-hydroxy-1,2,3-triazoles 190 (248). Reaction of 3 with isothiocyanates are strongly solvent dependent. 

Ketenes rarely produce [3+ 2]-cycloaddition products with diazo compounds. The reaction possibilities are complex, and nitrogen-free products are often obtained (5). Formation of a cyclopropanone represents one possibihty. Along these lines, the synthesis of (Z)-2,3-bis(trialkylsilyl)cyclopropanones and (Z)-2-trialkylsilyl-3-(triethylgermyl)cyclopropanones from diazo(trialkylsilyl)methanes and appropriate silyl- or germylketenes has been reported (256,257). It was found that subsequent reaction of the cyclopropanone with the diazoalkane was not a problem, in contrast to the reaction of diazomethane with the same ketenes. The high cycloaddition reactivity of diazomethylenephosphoranes also extends to heterocumulenes. The compound R2P(C1)=C=N2 (R = N(/-Pr)2) reacts with CS2, PhNCO and PhNCS to give the corresponding 1,2,3-triazole derivative (60). 

With nucleophilic bases 3,7,7a-trimethyl-2,3,5,6,7,7a-hexahydro-17f-imidazo[l,5-Zi][l,2,4]-triazole-2,5-dione (130) and -2,5-dithione (129) the [3 -H 2] cycloelimination of the heterocumulene moiety from the triazole ring is followed by nucleophilic addition of the base to give 4-substituted 4,5,5-trimethyl-2,3,4,5-tetrahydro-l/7-imidazol-2-ones (135) and -2-thiones (136), respectively (Scheme 7) <93TH 805-01, 95FES379). 

The reaction of l-arylamino-4,4-dimethyl-5-methylene-2,3,4,5-tetrahydro-l//-imidazol-2-one (338 Y = O) and -2-thione (338 Y = S) with protic heterocumulenes affords 7,7,7a-trimethyl-3-aryl-2,3,5,6,7,7a-hexahydro-l/7-imidazo[l,5-fe][l,2,4]triazol-2,5-diones (339 X = Y = 0), and N-and 5-derivatives of these functions in 2- and 5-positions (Equation (104)) <93TH 805-oi, 95FES379>. 

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