Neighboring effect by heteroaromatic rings: formation of skeletally rearranged adducts by cycloaddition reaction of norbornadiene-fused pyridazines and pyrazines with 4-phenyl-1,2,4-triazole-3,5(4H)-dione
作者:Tomoshige Kobayashi、Kiyomi Miki、Behrooz Nikaeen、Hideaki Baba
DOI:10.1016/s0040-4020(99)00821-2
日期:1999.11
Norbornadiene-fused pyridazines and pyrazines reacted with 4-phenyl-1, 2,4-triazole-3,5(4H)-dione to give skeletally rearranged adducts in moderate yields. A similar reaction with fused pyridazine N-oxides or a fused pyrazine N-oxide resulted in the regioselective formation of the rearranged adduct. The formations of the skeletally rearranged adducts would be ascribed to the intervention of bridged
Norbornadiene-Fused Heterocycles: Synthesis and Bromination Reaction of 5,8-Dihydro-5,8-methanoquinoxaline Derivatives
作者:Tomoshige Kobayashi、Kiyomi Miki
DOI:10.1246/bcsj.71.1443
日期:1998.6
A norbornadiene-fused pyrazine was prepared by the condensation reaction of bicyclo[2.2.1]hept-5-ene-2,3-dione with ethylenediamine followed by oxidation. Treatments of the norbornadiene-fused pyrazine and its benzo derivative with bromine in carbon tetrachloride or in dioxane afforded trans-adducts as major products, accompanied by the formations of cis-adducts and dibromo derivatives derived from Wagner–Meerwein type skeletal rearrangement, while bromination of a fused dicyanopyrazine in carbon tetrachloride gave only a trans-adduct. In contrast, a fused pyrazine with an electron-donating N-oxide group gave a 7,9-dibromo derivative as the main component. The possibility of the intervention of a 2H-pyrazinium ion for the formation of the skeletally rearranged products is discussed together with the results of ab-initio (3-21G*) calculations.