1,3-Dichloropropenes – in the preparation of thiazole derivatives – 2-chloro-5-chloromethylthiazole and 5-hydroxymethylthiazole

1,3-Dichloropropene (a mixture of cis and trans isomers) has been used to synthesize thiazole derivatives by starting its reaction with sodium thiocyanate to give 3-chloro-2propenylthiocyanate. This thiocyanate on heating undergoes thermal [3,3]-sigmatropic rearrangement to give the isothiocyanate derivative, 3-chloro-1-propenylisothiocyanate. This mixture of cis and trans isomers of isothiocyanate on chlorination gave 2-chloro-5chloromethylthiazole. 5-Hydroxymethylthiazole is made from 2-chloro-5-chloromethyl thiazole in two steps, first by displacement of the aliphatic halogen with formate anion followed by hydrolysis of the formate ester and hydrodehalogenation of the aromatic halogen using hydrogen and palladium on carbon catalyst.