E. Rosenberg, J. J. Zuckerman
Dec 16, 1971
Citations
0
Influential Citations
15
Citations
Journal
Journal of Organometallic Chemistry
Abstract
Abstract 2,2-Dimethyl-2-silanorcarane has been prepared by the stepwise reduction of 7,7-dibromo-2,2-dimethyl-2-silanorcarane with tri-n-butyltin hydride. Treatment of the dibromonorcarane with silver ion or pyrolysis with quinoline releases hydrogen bromide and decomposs the ring system. Trimethyl(dimethylamino)stannane reduces the dibromo compound to a 1.5/1 mixture of the endo - and exo -isomers of 7-bromo-2,2-dimethy-2-silanorcarane in the first known reaction of the tinnitrogen bond to proceed by a radical mechanism. β-Elimination of bromine is favored endo ⪢ exo in the mass spectrometer. The 7,7-dibromo compound is prepared by a series of steps which include the hydrosilation of 5-chloro-1-pentyne by trichlorosilane, the intramolecular Barbier cyclization of the product, the methylation of the resulting 1,1-dichloro-1-sila-2-cyclohexene, and the action of a dihalocarbene generated from phenyl(tribromomethyl)mercury on this silacyclohexene. The dibromonocarane is formed in 50% yield, but a side reaction produces 5-(dimethylbromosilyl)-1-pentene, which was identified as its hydrolysis product, [CH 2 CH)CH 2 ) 3 Si(CH 3 ) 2 ] 2 O. Deuteration experiments establish that the process of ring-opening is concerted, and the observation of resonances due to a transient β-addition product in the NMR leads to the proposal of an HBr-addition β-elimination mechanism for ring-opening which appears to apply to several examples of unsaturated sila- and germacarbocycles in general. Hydrostannation of 5-chloro-1-pentyne by dimethyltin hydride chloride leads to the dimethylchlorostannyl-substituted 5-chloro-1-pentene which undergoes alkyl group redistribution to form a mixture of alkyltin chlorides.