Stereochemical control factors in the Hantzsch thiazole synthesis: A Hammett substitution correlation analysis

[GRAPHICS] It is possible to correlate the distribution of stereochemical products pro duced during a Hantzsch thiazole synthesis according to the Hammett free-en ergy equation. This analysis confirms the presumed control of the rate of e pimerization during thiazole formation due to stabilization of a cationic t ransition state intermediate during dehydration of the thiazoline ring syst em. In the chemical system under study, the stereochemical outcome of the r eaction also appears to occur according to a kinetically controlled protona tion of a thiazoline tautomer.