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Wittig Reaction

The reaction of a tertiary phosphine (usually triphenylphosphine) with an alkyl halide to yield a phosphonium salt can be done in DMSO [McKinley, S. V.; Rakshys, J. W., Jr., J. Chem. Soc. Chem. Commun. 134-135 (1972)]. DMSO also seems to be a good solvent for these salts. In these phosphonium salts, C-H bonds are sufficiently acidic [House, H. O., Modern Synthetic Reactions, 2nd Edition, W.A. Benjamin Inc., Menlo Park, 682-691 (1972)] for the hydrogen to be removed by a strong base in DMSO, e.g. an organolithium compound [Bhalerao, U. T.; Rapaport, H., J. Am. Chem. Soc. 93, 105-110 (1971)], sodium hydride or the dimsyl ion [James, G. G.; Pattenden, G., J. Chem. Soc. Perkin Trans. 1, 1476-1479 (1976)], to produce a phosphorus ylide (a phosphorane), the so-called Wittig reagent. Subsequent reactions of these ylides with aldehydes, ketones or hemiacetals in DMSO offer a useful synthesis for olefins. The overall reaction can be written as follows [Fuqua, S. A.; Duncan, W. G.; Silverstein, R. M.,Tetrahedron Lett., 9, 521-523 (1965); Greenwald, R.; Chaykovsky, M.; Corey, E. J., J. Org. Chem. 28, 1128-1129 (1963); House, H. O., Modern Synthetic Reactions, 2nd Edition, W.A. Benjamin Inc., Menlo Park, 682-691 (1972)].

As mentioned above, the Wittig reaction converts carbonyl compounds to olefins. Thus, the reaction of formaldehyde and the phosphorane derived from 1 ,5-bis(triphenylphosphonomethyl)naphthalene dibromide in DMSO gives 1,5-divinylnaphthalene [Fleming, R. H.; Quina, F. H.; Hammond, G. S., J. Am. Chem. Soc. 96, 7738-7741 (1974)].

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