An efficient route to substituted 1-silacyclopent-2-enes and 1-silacyclohex-2-enes via consecutive 1, 2-hydroboration and 1,1-organoboration

The reaction of alkyn-1-yl(vinyl)silanes R2Si(C CR1)CH=CH2[R = Me (1), Ph (2); R-1 = Bu-t (a), Ph (b), SiMe3 (c)] with 9-borabicyclo[3.3.1]nonane in a 1:1 ratio affords the 1-silacyclopent-2-ene derivatives 4a-c (R = Me) and 5a-c (R = Ph) as a result of selective intermolecular 1,2-hydroboration. of the vinyl group, followed by intramolecular 1, 1-organoboration of the alkynyl substituent. The analogous reaction sequence converts the alkyn-1-yl(allyl)dimethylsilanes 3a,c into the 1-silacyclohex-2-ene derivatives 7a,c. All reactions were monitored by Si-29 NMR spectroscopy and the structural assignment of the final products was based on multinuclear magnetic resonance data (H-1, B-11, C-13 and Si-29 NMR). The molecular structure of 6a was determined by X-ray analysis. (c) 2005 Elsevier B.V. All rights reserved.