SYNTHESIS, REACTIONS, AND STEREOCHEMICAL STUDIES OF NEW BICYCLIC ORGANOSILICONS: 3-SILABICYCLO(3.2.1)OCTANES AND 2-SILABICYCLO(2.2.1)HEPTANES

Craig Blankenship, Marquette University

Abstract

Several members of two new classes of bicyclic organosilicons, 3-silabicyclo{3.2.1}octanes (3-SBO) and 2-silabicyclo{2.2.1}heptanes (2-SBH), were prepared by five- and seven-step synthetic sequences, respectively. Reaction of the bis-organomagnesium reagent of cis-1,3-bis(bromomethyl)cyclopentane with trichloromethylsilane, trichlorophenylsilane, or silicon tetrachloride was used to prepare derivatives of the 3-SBO system. Platinum-catalyzed intramolecular hydrosilation of 4-{(dichlorosilyl)methyl}cyclopentene or 4-{(chloromethylsilyl)methyl}cyclopentene gave access to the 2-SBH series. New compounds were characterized by elemental analysis, ('1)H and ('13)C NMR, IR, and/or mass spectrometry; ('29)Si NMR spectra were obtained for 3-SBO, endo- and exo-3-methyl-3-SBO, 2-SBH, and endo- and exo-2-methyl-2-SBH. A unique mode of fragmentation was observed in the mass spectra of the isomers of 3-methyl-3-SBO involving loss of H(,2); this fragmentation gave the base peak in the spectrum of exo-3-methyl-3-SBO, whereas a corresponding peak of low intensity was observed for endo-3-methyl-3-SBO. Electron diffraction analyses were obtained for 3-SBO and endo-3-methyl-3-SBO; the latter analysis provided an unambiguous isomer assignment which was extended to six other isomer pairs in the 3-methyl-3-SBO series through correlation of several physical properties. Isomers of 2-methyl-2-SBH derivatives were assigned from the NMR spectral properties. The stereochemistry of several reactions of 3-methyl-3-SBO derivatives was studied; the results paralleled those observed for acyclic organosilicons. Studies of the stereochemistry of reactions of 2-methyl-2-SBH derivatives were initiated. LAH reduction of 3-chloro-3-methyl-3-SBO occurred with inversion of configuration, but the stereochemistry of reduction of 2-chloro-2-methyl-2-SBH was more complex. The isomers of 3-methyl-3-SBO, 3-methoxy-3-methyl-3-SBO, 3-methyl-3-phenyl-3-SBO, and 2-methyl-2-SBH were equilibrated by treatment with CsF in polar, aprotic solvents; (+)-(alpha)-naphthylphenylmethylsilane (I) was also readily racemized. The order of reactivity toward isomerization was I > 2-methyl-2-SBH(TURN)3-methoxy-3-methyl-3-SBO > 3-methyl-3-SBO > 3-methyl-3-phenyl-3-SBO. Isomerization of 3-methyl-3-SBO was examined with respect to the nature of the fluoride salt, solvent, and added crown ether. The proposed mechanism involves reversible formation of a pentacoordinate intermediate which can undergo pseudorotation.

Recommended Citation

Craig Blankenship, "SYNTHESIS, REACTIONS, AND STEREOCHEMICAL STUDIES OF NEW BICYCLIC ORGANOSILICONS: 3-SILABICYCLO(3.2.1)OCTANES AND 2-SILABICYCLO(2.2.1)HEPTANES" (January 1, 1982). Dissertations (1962 - 2010) Access via Proquest Digital Dissertations. Paper AAI8217280.
http://epublications.marquette.edu/dissertations/AAI8217280

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