Synthesis and structure of novel spirosilanes. Combination of 1,2-hydroboration and 1,1-organoboration

The reaction of tetra(alkyn-1-yl)silanes Si(C C-R-1)(4) 1 [R-1 = Bu-t (a), Ph (b), C6H4-4-Me (c)] with 9-borabicyclo[3.3.1]nonane (9-BBN)in a 1 :2 ratio affords the spirosilane derivatives 5a-c as a result of twofold intermolecular 1,2-hydroboration, followed by twofold intramolecular 1,1-organoboration. Intermediates 3a-c, in which two alkenyl- and two alkyn-1-yl groups are linked to silicon, were identified by NMR spectroscopy. The molecular structure of the spiro compound 5c was determined by X-ray analysis, and the solution-state structures of products and intermediates follow conclusively from the consistent NMR spectroscopic data sets (H-1, B-11, C-13 and Si-29 NMR). Copyright (C) 2008 John Wiley & Sons, Ltd.