Preparation and some chemistry of alpha-halo and alpha-diazo sulfoxides

Abstract

The addition of diazo alkanes to sulfinyl chlorides yields alpha-chloro sulfoxides in good yields and uncontaminated by positional isomers which result when unsymmetrical dialkyl sulfoxides are chlorinated in the presence of base. The presence of alkali halide salts in the diazo alkane solution diverts the product to the alpha-halo sul oxide bearing the anion of the added salt. This procedure is particularly useful for the preparation of alpha-iodo sulfoxides. Addition of benzenesulfinyl chloride to a molar excess of diazomethane in tetrahydrofuran at -78° yields a 2:1 mixture of benzenesulfinyl diazomethane and phenyl chloromethyl sulfoxide. The diazo sulfoxide is extremely unstable, decomposing above -20°. Evidence for the diazo structure was obtained from its spectra and chemical reactions. Low temperature (-30°) removal of solvent yields an oil which has a strong absorption at 2040cm^-1 in its infrared spectrum. The NMR spectrum has a sharp singlet at delta 5.5 ppm, which was assigned to the resonance of the methine proton on the diazo bearing carbon. In addition, the resonances due to phenyl chloromethyl sulfoxide were observed. Treatment of the reaction mixture containing the alleged diazo sulfoxide with HBr or HI gives approximately a 2:1 mixture of phenyl bromomethyl or phenyl iodomethyl sulfoxides, respectively, and phenyl chloromethyl sulfoxide. Thermal decomposition of the reaction mixture in Z-2-butene yielded anti-cis-1,2-dimethyl-3-benzenesulfinyl cyclopropane (42.5%), syn-cis-1,2-dimethyl-3-benzenesulfinyl cyclopropane (0.03%), anti/syn = greater than 99:1, phenyl chloromethyl sulfoxide (40.5%), and phenyl disulfide (4.00/4). Trans-1,2- dimethyl-3-benzenesulfinyl cyclopropane was not detected in the HPLC chromatograms of the reaction mixture. Thus, cyclopropanation of Z-2-butene proceeded with exclusive cis-stereospecificity. Copper(I)chloride catalyzed decomposition of the reaction mixture in cyclohexene at -78° gave anti-7- benzenesulfinyl norcarane (40%}, phenyl chloromethyl sulfoxide (38%), bis(benzenesulfinyl)ethylene (12%}. Syn-7-benzene sulfinyl norcarane was not detected by HPLC analysis of the reaction mixture. Thermal decomposition of the diazo sulfoxide in cyclohexene yielded anti-7-benzenesulfinyl norcarane (52%), syn-7-benzenesulfinyl norcarane (0.09%), anti/syn = 34: 1, and phenyl chloromethyl sulfoxide (36.5%). No C-H insertion products were observed in any of the above reactions. The unprecedented degree of anti-stereoselectivity and the absence of C-H insertion, products observed in the cyclopropanation reaction was postulated to be a result of two factors: first, the sulfinyl function imparts considerable bulk to the adjacent divalent carbon; second, the carbene is stabilized via resonance interaction of the sulfinyl sulfur lone pair with the empty . p-orbital on carbon.