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(CCR1)CHCH2 [R = Me (1), Ph (2); R1 = tBu (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 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.

Graphical abstractAlkyn-1-yl(vinyl)silanes R2Si(CCR1)CHCH2 [R = Me, Ph; R1 = tBu, Ph, SiMe3 and alkyn-1-1yl(allyl)silanes react with 9-borabicyclo[3.3.1]nonane in a 1:1 ratio ro give 1-silacyclopent-2-ene derivatives and 1- silacyclohex-2-ene derivatives, respectively. This is the result of selective intermolecular 1,2-hydroboration of the vinyl or allyl group, followed by intramolecular 1,1-organocarboration of the alkynyl substituent.Figure optionsDownload full-size imageDownload as PowerPoint slide