2-Chloro-5-bromothiazole

The mixed 2-chloro-5-bromothiazole has been obtained from 2-amino-5-bromothiazole, as previously indicated (75). 

Bromothiazoles were more reactive than their chloro analogs. For example, 2,4-di-bromo-5-(hydroxymethyl)thiazole was completely debrominated to give 5-(hy-droxymethyl)thiazole in 94% yield at 23 °C for 12 h, while the corresponding dichloro analog gave only 28% yield of 5-(hydroxymethyl)thiazole even at 60°C for 60 h the major product was 4-chloro-5-(hydroxymethyl)thiazole (63%). 

An operationally simple halogenation of 4,5-dimethyl-2-arylthiazoles provides a regioselective approach to bromo- or chloro-methyl substituted thiazoles <04TL69>. Thus, treatment of 117 and its hydrochloride salt with NBS and NCS affords 4-bromothiazole 118 and 4-chlorothiazole 119, respectively, with >99% regioselectivity. The remarkable regioselectivity observed may arise from a Pummerer-type rearrangement mechanism via 120. 

Preparative Method although 2-(trimethylsilyl)thiazole (1) is commercially available, it can be easily prepared on a multigram scale from 2-bromothiazole, n-butyUithium, and chloro-trimethylsilane as shown in eq 1. ... 

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