Reactions of Donor Acceptor Cyclopropanes with Naphthoquinones: Redox and Lewis Acid Catalysis Working in Concert

Reactions of 2-arylcyclopropane dicarboxylates with naphthoquinones are reported. The key feature was the use of catalytic amounts of SnCl2, which acts as both an electron donor and a 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 condhions resulted through loss of methyl formate in cyclopenuumulated products with fully conjugated pi Systems exhibiting intensive absorptions in the visible range.