Redox troponization as a novel method for the synthesis of stereoisomeric Eschenmoser's oximes and related non-benzenoid aromatic systems
A novel method for the synthesis of the oxime of 4-methyl-2,4,6-cycloheptatrien-1-one (Eschenmoser's oxime) is proposed. The method involves redox enlargement of the ring of 4-dibromomethyl-4-methyl-2,5-cyclohexadien-1-one oxime through the action of Ni(PPh3)4 in DMF (in the presence of Zn). The product is formed as a mixture ofsyn- andanti-forms readily interconverting in solutions. A similar reaction of 4-methyl-4-trichloromethyl-2,5-cyclohexadien-1-one oxime afforded the dimer of agem-α-centered semiquinoid carbene (1,2-bis-(1-methyl-4-oxyimino-2,5-cyclohexadienyl)-1,2-dichloroethylene), together withsyn- andanti-isomers of 4-chloro-5-methyl-2,4,6-cycloheptatrien-1-one oxime, which are readily separable but also quickly interconverting in solutions. For the latter compounds, the complete1H NMR assignment of the stereoisomeric structures has been carried out.
Key wordsnon-benzenoid aromatic compounds tropones troponoximes Pd0 complexes in organic synthesis
Unable to display preview. Download preview PDF.
- 1.I. L. Buchanan and D. R. Lockhart,J. Chem. Soc., 1959, 3586.Google Scholar
- 2.T. Nozoe,Pure & Appl. Chem., 1982.54(5), 975.Google Scholar
- 3.T. Machiguchi, H. Otani, Y. Ishii, and T. Hasegawa,Tetrahedron. Lett., 1987,28, 203.Google Scholar
- 4.J. Schreiber, M. Pesaro, W. Leimgruber, and A. Eschenmoser,Helv. Chim. Acta., 1958,41(7), 2103.Google Scholar
- 5.V. A. Nikanorov, G. V. Gavrilova, S. V. Sergeev, V. I. Rozenberg, and O. A. Reutov,Metalloorg. khim., 1989,2(1), 102 [Organomet. Chem. USSR, 1989,2(1) (Engl. Transl.)].Google Scholar
- 6.M. Makosza and N. Wawrzyniewich,Tetr. Lett., 1969, (53), 4659.Google Scholar
- 7.M. Barbier, D. H. Barton, M. Devys, and R. S. Topgi,Tetrahedron, 1987,43(21), 5031.Google Scholar
- 8.V. I. Bakhmutov, M. V. Galakhov, V. A. Nikanorov, G. V. Gavrilova, V. I. Rozenberg, and O. A. Reutov,Dokl. Akad. Nauk SSSR, 1987,295(6), 1376 [Dokl. Chem., 1987,295(6) (Engl. Transl.)].Google Scholar
- 9.G. R. Underwood and K. El Bayoumy,J. Am. Chem. Soc., 1982,104, 3007.Google Scholar
- 10.T. Zincke, R. Suhl,Ber., 1906,39, 4148.Google Scholar
- 11.G. V. Gavrilova, V. I. Bakhmutov, V. I. Rozenberg, V. A. Nikanorov, A. A. Gavrilov, and O. A. Reutov,Metalloorg. khim., 1990,4(2), 299 [Organomet. Chem USSR, 1990,4(1) (Engl. Transl.)]Google Scholar
- 12.M. Cobreros, F. Jato, E. Ravina,Chim. Ther., 1973,8(4), 896.Google Scholar