Effect of various substituents on intramolecular 1,1-vinylboration, synthesis of 1-silacyclobutene derivatives

摘要

The reaction of 1-boryl-1-alkenyl chlorosilane derivatives with alkynyllithium reagents [Li-C ≡ C-R~3 (R~3 = Ph, SiMe3)] at low temperature (-78 °C) affords alkenyl(alkyn-1-yl)silanes. These compounds are precursors of 1-silacyclobutene derivatives, which are formed via intramolecular 1,1-vinylboration. This reaction works for various groups at silicon (R~1 /R~2: R~1 = H, Me, Ph; R~2 = Me, Ph) and at the C=C and C ≡ Cunits (R/R~3: R=~nBu,Ph;R~3 = ~nBu, Ph, SiMe3) . The conversion into 1-silacyclobutene derivatives is incomplete only in the case of R~3 = SiMe3 . The reactions were monitored by NMR spectroscopy in order to elucidate the reaction mechanism, and the proposed structures of all new compounds follow from consistent sets of NMR parameters (~1H-, ~(13)C-, ~(11)B-, ~(29)Si-NMR).