Triazolines, synthesis, sodium azide

The synthesis of 4,5-disubstituted triazoles shown in Scheme 208, carried out on a polymer support with microwave assistance, is based on a similar principle. In the first step, sulfinate 1248 is converted to sulfone 1249. Condensation with aldehydes provides vinyl sulfones 1250. Cyclocondensation of sulfones 1250 with sodium azide generates corresponding triazoline intermediates that eliminate sulfinate 1248 to provide triazoles 1251 in moderate to good yield <2006OL3283>. 

The first synthesis of the parent compound of the benzo[4,5]thieno[2,3-f]pyrrole ring system 387 <2003T1477> and its derivatives was accomplished using the same synthetic sequence (Scheme 42). Starting with 2-methyl-benzo[ ]thiophene-3-carbaldehyde 388, an intermediate 389 was obtained. Treatment of bromo compound 389 with sodium azide in ethanol led to the stable triazoline 390. 1,3-Dipolar cycloreversion of 390 was induced by a catalytic amount of />-TsOH to give the parent 2//-benzo[4,5]thieno[2,3-c]pyrrole 387. Alternatively, direct treatment of bromo compound 389 with excess ammonia furnished 387 in one step. Compound 387 was treated with di-/-butyl dicarbonate and 4-dimethylaminopyridine (DMAP) to give iV-BOC derivative 391. Reaction of 389 with... 

An interesting application of this process to synthesis is Hudlicky s preparation of several pyrrolizidine alkaloids via treatment of conjugated ketone 491 with sodium azide (NaNs) to give keto-azide 492 in 88% yield.383 Addition of the azide to the diene apparently generates a triazoline, which was not isolated but... 

Furin et al. (2001) published a method for the synthesis of 4,4-bis(trifluoromethy 1)-5-ethoxy-5-pentafluoroethyl-l,2,3-triazoline 63 based on the electrocyclic cycliza-tion of linear vinyl azide as a precursor [68], In the first stage of this process the perfluoro-2-methyl-2-pentene reacted with sodium azide in acetonitrile-ethanol mixture at -20 °C furnishing the vinyl azide, which at -10 C underwent an intramolecular cyclizalion into an unstable intermediate 64. In the presence of ethanol a nucleophiUc attack of ethoxy anion on C=N bond of intermediate 63 occurs to form a stable product 64 [68],... 

Buchanan et al. (48) reported a new route to the synthesis of the chiral hydroxy-pyrrolidines 234 and 238 from D-erythrose (230) via an intramolecular cycloaddition of an azide with an alkene (Scheme 9.48). Wittig reaction of the acetonide 230 with (carbethoxyethylene)triphenylphosphorane gave the ( ) and (Z) alkenes 231 and 232. On conversion into the triflate followed by its reaction with KN3, the ( ) isomer 231 allowed the isolation of the triazoline 234 in 68% overall yield, which on treatment with sodium ethoxide afforded the diazo ester 235 in 86% yield. 

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