We report a mild
Lewis acid induced isomerization of donor–acceptor
cyclopropanes, containing an alkenyl moiety and diverse electron-withdrawing
group(s) at the adjacent positions, into substituted cyclopentenes.
We have found that 1,1,2-trisubstituted cyclopent-3-enes were exclusively
obtained in yield of 51–99% when cyclopropanes with a 2-substituted
alkenyl group as a donor underwent isomerization. For cyclopropanes
bearing a trisubstituted alkenyl group either the corresponding cyclopent-3-enes
or isomeric cyclopent-2-enes having two acceptor groups at the C(1)
atom were formed, with the reaction selectivity being determined by
the applied Lewis acid. We have shown that the reactivity of the donor–acceptor
cyclopropane increases with the increase of the electron-donating
character of (hetero)aromatic group attached to the alkenyl moiety.
The synthetic utility of the developed methodology was also demonstrated
through the synthesis of polysubstituted cyclopentane and piperidine
derivatives