Pyrimidine reactions. XXVI. 2-(1'-Bromo-1'-methylethyl)pyrimidines: Synthesis, solvolysis and dehydrobromination to 2-Isopropenylpyrimidines

Abstract

Synthetic routes to 2-isopropyipyrimidine (2b) and to its 4-phenyl and 4-methoxy derivatives, (2e) and (2h), are outlined. These pyrimidines undergo α-bromination by N-bromosuccinimide to give the 2-(1?-bromo-1?- methylethyl)pyrimidines (2c), (2f) and (2i) respectively. In methanol, controlled at neutrality, these bromo derivatives give the corresponding 1?-methoxy compounds (2j-l) but in methanolic sodium methoxide, each undergoes dehydrobromination to the appropriate 2- isopro-penylpyrimidine (3; R = H, Ph or OMe): these are confirmed as olefins by N.M.R. spectra and by the conversion of the second (3; R = Ph) into its epoxide (4). First-order rate constants for solvolysis of the bromo derivatives in 50% aqueous methanol, maintained at apparent pH 7.0, are recorded and discussed.