Complexes of Donor–Acceptor Cyclopropanes with Tin, Titanium, and Gallium Chlorides — Mechanism Studies

Abstract

Hitherto unknown complexes of dimethyl cyclopropane-1,1-dicarboxylate with Lewis acids (Sn, Ti, and Ga chlorides) have been isolated and characterized. Their structures, which were previously assumed from theoretical considerations, have been confirmed, and the activating effect of Lewis acids on the cyclopropane ring has been shown experimentally. A single crystal of the complex with SnCl4 has been obtained, and an X-ray diffraction study has been performed. Hitherto unknown complexes of donor–acceptor cyclopropanes with GaCl3 belonging to a new type and having a 1,2-dipole (ylide) structure have been obtained and characterized. 1D and 2D NMR spectroscopy on 1H, 13C, 35Cl, 71Ga, and 119Sn nuclei were used to study the structures of the complexes. Furthermore, DOSY diffusion NMR spectroscopy was used to determine the diffusion coefficient in solution and the molecular masses of the complexes. The data obtained enrich the picture of transformations of donor–acceptor cyclopropanes widely used in organic synthesis. The practical use of the gallium phenylcyclopropanedicarboxylate complex in a synthesis of polysubstituted cyclic structures in one synthetic stage has also been demonstrated.