Synthesis and molecular structures of 1-chloro-1-silacyclopent-2-enes. Combination of 1,2-hydroboration, 1,1-organoboration and protodeborylation

Abstract

The reaction of alkyn-1-yl(chloro)(methyl)vinyl- and alkyn-1-yl(chloro) (phenyl)-vinylsilane with 9-borabicyclo[3.3.1]nonane (9-BBN) afforded selectively 1-silacyclopent-2-ene derivatives containing a Si-Cl function, as a result of consecutive 1,2-hydroboration and 1,1 -organoboration. Protodeborylation with acetic acid left the Si - Cl functions in various 1-silacyclopent-2-enes untouched, whereas acetic acid in the presence of dipropylamine led to conversion of the Si-Cl into the Si-OAc function. New starting materials and all products were characterized in solution by multinuclear NMR spectroscopy (1H, 11B, 13C and 29Si NMR), and the molecular structures of two 1-silacyclopent-2-ene derivatives were determined by X-ray analysis. The gas phase geometries of 1-silacyclopent-2-enes were optimized by DFT calculations [B3LYP/6-311+G(d,p) level of theory], found to be in reasonable agreement with the results of the crystal structure determination, and NMR parameters were calculated at the same level of theory. Copyright © 2009 John Wiley & Sons, Ltd.