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

Abstract

The reaction of alkyn-1-yl(vinyl)silanes R 2Si(C CR 1)CH CH 2 [R = Me ( 1), Ph ( 2); R 1 = t Bu ( a), Ph ( b), SiMe 3 ( 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 29Si NMR spectroscopy and the structural assignment of the final products was based on multinuclear magnetic resonance data ( 1H, 11B, 13C and 29Si NMR). The molecular structure of 6a was determined by X-ray analysis.