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

摘要

The reaction of 1-boryl-1-alkenyl chlorosilane derivativeswith alkynyllithium reagents [Li-Cequiv C-R^3 (R^3~=~Ph, SiMe_3)] atlow temperature (--78 °C) affords alkenyl(alkyn-1-yl)silanes. Thesecompounds are precursors of 1-silacyclobutene derivatives, which areformed via intramolecular 1,1-vinylboration. This reaction works forvarious groups at silicon (R^1/R^2: R^1 = H, Me, Ph; R^2 = Me, Ph) andat the C=C and Cequiv C units (R/R^3: R = ^nBu, Ph; R^3 = ^nBu, Ph,SiMe_3). The conversion into 1-silacyclobutene derivatives isincomplete only in the case of R^3 = SiMe_3. The reactions weremonitored by NMR spectroscopy in order to elucidate the reactionmechanism, and the proposed structures of all new compounds followfrom consistent sets of NMR parameters (^1H-, ^{13}C-, ^{11}B-,^{29}Si-NMR).