2.5- Dimethylthiazole, cycloaddition with

Thiazole itself reacts with DMAD at room temperature in DMF, the initially formed adduct (88) rearranging either via a concerted suprafacial 1,5-sigmatropic shift or by a non-concerted pathway proceeding via zwitterion (89) to (90 R = R = H Scheme 50) (79HC(34-i)i, p. 97). The three monomethylthiazoles and 2,5-dimethylthiazole undergo the same type of cycloaddition with rearrangement when condensed with DMAD in DMF (Scheme 50 R,R = Me, H H, Me-4 H, Me-5 Me, Me-5). 

Solvent has an important influence on the course of this cycloaddition, and in the reaction of 2,5-dimethylthiazole with DMAD in DMF the product analogous to (415) was obtained. However, in DMSO or acetonitrile a thiazolo[3,2-a]azepine was formed in addition to this product, whereas with THF, dichloromethane or nitromethane, only the thiazoloazepine was isolated. 

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