Theoretical confirmation of the reaction mechanism leading to regioselective formation of thiazolidin-4-one from bromoacetic acid derivatives

A regioselective synthesis of 3-alkyl-2-[(anthracen-9-yl)imino]thiazolidin-4-ones 2a-2e and 2-(alkylimino)-3-(anthracen-9-yl)thiazolidin-4-ones 3a-3e from appropriate thioureas using methyl bromoacetate or bromoacetyl bromide, respectively, has been rationalized by DFT calculations of model thiourea and its phenyl derivative. The proposed mechanism indicates that the regioselective formation of the target thiazolidinones is a consequence of a different reactivity of the reagents and a varying stability of the intermediates, 1-alkyl-3-(anthracen-9-yl)-2-[(methoxycarbonyl)methyl]isothioureas 4a-4e and 1-alkyl-3-(anthracen-9-yl)-2-(bromoacetyl) isothioureas 6a-6e.