Intramolecular nucleophilic attack by urea nitrogen. Reactivity–selectivity relationships for the general acid–base catalysed cyclisations of ureido acids and esters

Abstract

The cyclisation of N-substituted hydantoic acids involves general acid–base catalysed attack of urea nitrogen on the CO₂H group. The variation of the Brønsted exponents for the reactions of the N-methyl and N-phenyl derivatives (2) and (3) allows a choice between kinetically equivalent mechanisms. Stereoelectronic effects on the nucleophilic reactions of urea NH are considered, and a mechanism involving an initial rotation about the terminal C–N bond of the ureido group is suggested.