Of 2-azidothiazoles

A study of the relative stability of tra 5-2-azidothiazole 32b with respect to the corresponding cis conformer 32a showed that 32b is destabilized in the gas phase but appears to be the more stable conformer in solution (Scheme 23). The stability increases with increasing polarity of the solvent [98JA4723]. 

The aminolysis of turns-1,2-bis(ethylsulfonyl)-1.2-dichlorocthcnc (336) by primary and secondary aliphatic amines in acetonitrile has been studied.305 Thermolysis in p-xylene solution of 4-azidothiazoles (337) displayed some interesting neighbouring-group effects,306 e.g. in (337) with R1 = Ph, R2 = (acceleration produced in parentheses) NO2 (19-fold), phenyliminomethyl (16-fold), formyl (4.5-fold), and acetyl (2.2-fold). Rate data for nucleophilic attack on phenyldimethylsulfonimn ions by... 

Whereas in the gas phase and in nonpolar solvents sueh as tetraehloromethane and benzene, the 2-azidothiazole (38a) is the more stable isomer, in polar solvents such as dimethyl sulfoxide and hexamethylphosphorie triamide the bieyelie valenee isomer (38b) is the dominant speeies [100]. This result is in line with the faet that the dipole moment of phenyl azide g = 5.2 10 Cm) is smaller than that of cyclie 1,2,3-benzotriazole (// = 13.7 10 Cm). Similar results have been obtained for the valenee isomers of 3-azidopyrazine-l-oxide [204]. 

Heating of 4-azidothiazoles having an imino or aldehyde group at the 5-position affords fused pyrazolo- and isoxazolo[3,4-rf]thiazoles (Equation (30)). When an alkenyl group is in 5-position of the thiazole ring, 4/r-pyrrolo[2,3-cf]thiazoles are obtained <92JCS(P1)973>. 

Azide-tetrazole tautomerism has been investigated by n.m.r. spectroscopy and dipole-moment measurements for the 2-azidothiazole system, (801) (802), and for 2-azidobenzothiazole, 2-azidobenzoxazole, and 3-azidoisoxazole. Chlorosulphonation of the tetrazolobenzothiazole (803) with chlorosulphonic acid yields 2-azido-6-chlorosulphonyl-benzothiazole. ... 

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