Pathways of reactions of 2-arylcyclopropane-1,1-dicarboxylates with monosubstituted cycloheptatrienes under the action of GaCl3

Abstract

The reaction of 2-arylcyclopropane-1,1-dicarboxylates (ACDCs) with the unsaturated cyclohepta-2,4,6-triene-1-carboxylate system under the action of GaCl₃ proceeds with a contraction of the seven-membered cycle and formally corresponds to the [2+4] or [3+2] cycloaddition of 1,2- or 1,3-zwitterionic intermediates generated from ACDCs to the double bonds of the norcaradiene structure. On the contrary, cycloheptatrienes with donor substituents practically do not form cycloaddition products in reactions with 1,2-zwitterionic intermediates, but undergo dehydrogenation and significant oligomerization. Methyl- and phenylcycloheptatriene turned out to be rather good precursors of hydride ions, which resulted in the formation of (2-phenylethyl)malonate, while 7-methoxycycloheptatriene predominantly transforms the 1,2-zwitterion open form to the initial ACDC.