Atmosphere Effects on Arene Reduction with Lithium and Ethylenediamine in THF

Birch reductions employing lithium metal have been performed
mostly
under argon due to concerns about forming metal nitrides from the
reduction of dinitrogen if performed under nitrogen. Although it is
generally understood that inert atmospheres are standard for Birch
and Birch-type (lithium, ethylenediamine, t-BuOH,
THF) reductions, the atmosphere effect on Birch reduction has not
been studied. Herein, we report the reduction of model substrates
using lithium metal and ethylenediamine in THF under various atmospheric
conditions. The reductions under argon and nitrogen atmospheres afforded
essentially the same yields. Surprisingly, oxygen not only perturbed
the yields in some cases but also controlled regioselectivity for
a subset of naphthalenes. We propose a mechanism underlying the unexpected
oxygen-dependent regioselectivity for the Birch-type reduction of
naphthalenes. This work shows that the Birch-type reduction may be
performed under a nitrogen atmosphere and may account for a fraction
of oxygen-sensitive Birch-type reductions.