Reactions of 2-aryl cyclopropane dicarboxylates with
naphthoquinones are reported. The key feature was the use of
catalytic amounts of SnCl2, which acts as both electron donor and
Lewis acid. By an in-situ umpolung of naphthoquinone the formerly
electrophilic species is converted into a nucleophile that is able to
trigger the ring-opening of the three-membered ring with formation of
a new C-C bond. Treatment of these products with base under
oxidative conditions resulted - by losing methyl formate - in
cyclopentannulated products with fully conjugated π systems
exhibiting intensive absorptions in the visible range
