Spectrometric and chemical studies of 5-acyl- and 5-nitroso-2-(N,N-disubstituted amino)thiazoles

The conformational preferences of 2-(N,N-disubstituted amino)thiazoles having a 4-substituent (R1) and a 5-acyl group (R2CO) have been established by i.r. spectrometry and a crystallographic examination. In solution the compounds with R2= aryl and R1= Me or aryl exist predominantly or entirely in the carbonyl O,S-anti arrangement; for those with R1= aryl and R2= Me the syn rotamer is the main form but a small amount (ca. 15%) of the anti rotamer is present.Nitrosation of 4-aryl-2-dimethylaminothiazoles gives 5-nitroso derivatives, and these are probably the first authentic nitrosothiazoles. The barrier to rotation of the dimethylamino group is unexpectedly high (ΔG298‡= 69 kJ mol–1), exceeding even that of the 5-trifluoroacetyl analogues.