A Novel Synthesis of Methyl 1,5-Disubstituted Imidazole-4-carboxylates Using 3-Bromo-2-isocyanoacrylates (BICA)
摘要:
Methyl 1,5-disubstituted imidazole-4-carboxylates 1 were synthesised using methyl 3-substituted 3-bromo-2-isocyanoacrylates 3 (BICA), and the reaction mechanism was elucidated. Reactions of 3, which were prepared by bromination of 3-substituted 2-(formylamino)acrylates 6 followed by dehydration of the formylamino group, with a variety of primary amines gave imidazoles 1 in good overall yields. A mechanistic study suggested a Michael reaction of an amine with 3 followed by p-elimination of hydrogen bromide exclusively afforded (E)-N,3-disubstituted 3-amino-2-isocyanoacrylates 2. Geometric isomerization to (Z)-2 with a base and subsequent cyclization gave imidazoles 1.
Characterization of α-halo-imine intermediates derived from halogenation of dehydroamino acid derivatives
作者:Andrew P. Combs、Robert W. Armstrong
DOI:10.1016/s0040-4039(00)79004-6
日期:1992.10
An efficient one-pot Erlenmeyer-Plochl reaction affords high yields of optically active aliphatic dehydroamino acid derivatives. Subsequent halogenation with NBS or NIS yields the alpha-halo-imine derivatives which undergo kinetically controlled tautomerization with Et3N, resulting in increased E selectivity. Isomerization of these derivatives in the presence of strong base (DABCO) results in exclusive formation of the more stable Z vinyl bromides. High yields of the beta-halo-dehydroamino acids are obtained in all cases.