The role of the ester group in determining the regiochemistry of selected β-amino and β-ammonio radical cyclisations: generation of 1-azabicyclo[3.2.1]octyl- and -[2.2.2]octyl systems

Abstract

A comparison of the behaviour of the 2-(1,2,5,6-tetrahydro-3-methoxycarbonyl-1-pyridyl)ethyl radical and its quaternary N-methyl derivative shows that the latter is more conducive to cyclisation. These reactions display little regioselectivity, and significant quantities of both bicyclo[3.2.1]- and -[2.2.2]octanes are produced in each case. In contrast, an investigation of the quaternary 2-(4-ethoxycarbonylmethylene-1-pyridyl)ethyl radical, a modified hept-6-enyl-type radical, demonstrates that ring closure of this system provides a convenient, high-yielding route to quinuclidinium derivatives.