Although heating 2-methoxy-2H-azepine results in a [1,5] sigmatropic hydrogen shift, heating 2-propylthio-2H-azepine results in not only a [1,5] sigmatropic hydrogen shift but also a [1,5] sigmatropic propylthio shift. Kinetic measurements reveal that migratory aptitudes increase in the order of MeO < H, PrS. These [1,5] sigmatropic shifts are discussed on the basis of ab initio DFT calculations. [reaction:
Formation of 2-bromo-4-t-butyl-7-methoxy-2H-azepine and 4-t-butyl-7-methoxy-2-succinimidyl-2H-azepine by the respective reactions of 5-t-butyl-2-methoxy-3H-azepine with bromine and NBS suggests a plausible mechanism for the conversion of 3H-azepine to 2H-azepine as 1,4-addition of an electrophile and a consequent 1,2-dehydrobromination. Different from the case of cycloheptatriene, reaction of 3H-azepine with bromine did not give any delocalized ionic species.
Synthesis of a Delocalized Azepinium Ion and Investigation of Its Electrophilic Character
作者:Kyosuke Satake、Yasuhiro Kubota、Christopher E. J. Cordonier、Hideki Okamoto、Masaru Kimura