Donor-acceptor bicyclopropyl configuration-fixed by an additional trimethylene bridge: synthesis and Lewis acid-catalyzed tandem three-membered rings opening.

A diastereoselective synthesis of donor-acceptor bicyclopropyl, 8-phenyldispiro[2.3.2.0]-nonane-1,1-dicarboxylate, was carried out, which treated with Lewis acids acts as a synthetic equivalent of cis-1,6-zwitterionic intermediates. In the presence of GaCl3, the main direction is 1,6-cyclization to the substituted 1,2,3,4,6,7-hexahydro-5H-indene, while the action of EtAlCl2 triggers the three-membered rings opening, leading to the ethylation at the carbocation center. The reaction of 8-phenyldispiro[2.3.2.0]nonane-1,1-dicarboxylate with 4-phenyl-1,2,4-triazoline-3,5-dione in the presence of 10 mol.% of Yb(OTf)3 proceeds through the ionic [6+2] cycloaddition of 1,6-zwitterion to the N=N bond with the formation of an eight-membered heterocycle. [ABSTRACT FROM AUTHOR]