Nitration of α,β-unsaturated esters. Evidence for positive charge build-up adjacent to carbonyl carbon
作者:Stuart A. Hewlins、John A. Murphy、Jian Lin、David E. Hibbs、Michael B. Hursthouse
DOI:10.1039/a607170h
日期:——
Reactive intermediates formed in the nitration of certain
α,β-unsaturated esters with nitronium tetrafluoroborate
exhibit behaviour expected of highly reactive α-carbonyl cations.
Three diagnostic reaction types have been observed which indicate the
presence of these destabilised cations: (i) trapping in a Ritter
reaction, (ii) cyclopropane formation from propyl cations, (iii)
WagnerâMeerwein migration of alkyl groups. Semi-empirical
calculations of the relative gas-phase stabilities of the proposed
intermediate cations are useful in rationalising the observed
chemistry.
在用四氟硼酸亚硝酰进行某些α,β-不饱和酯的硝化反应中形成的活性中间体表现出高度活性α-羰基阳离子的预期行为。已观察到三种诊断性的反应类型,表明这些不稳定的阳离子的存在:(i)在Ritter反应中捕获,(ii)从丙基阳离子形成环丙烷,(iii)烷基的Wagner-Meerwein迁移。对所提出的中间阳离子的相对气相稳定性的半经验计算有助于合理化观察到的化学现象。