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.
β-Functionalized α,β-unsaturated amino acids were synthesized by an addition-elimination pathway. Reaction of methyl β-bromo-α-formylaminoacrylates (3a-e), which were prepared by the condensation of methyl isocyanoacetate (1) with aldehydes followed by bromination, with thiols gave β-alkylthio-α, β-unsaturated amino acidderivatives (6a-f). The reaction of (3a) with sodium azide resulted in the formation
Various methyl 1,5-disubstituted imidazole-4-carboxylates are synthesized by the reaction of methyl 3-bromo-2-isocyanoacrylates with a variety of primary amines in the presence of triethylamine.