Combination of 1,2‐Hydroboration and 1,1‐Organoboration: A Convenient Route to 5‐Silaspiro[4,4]nona‐1,6‐diene Derivatives

Abstract

Dialkyn-1-yl(divinyl)silanes were prepared and their reactions with 9-borabicyclo[3.3.1]nonane (9-BBN) were studied. 1,2-Hydroboration takes place selectively at the vinyl group, followed by intramolecular 1,1-organoboration to form a 1-silacyclopent-2-ene ring. Repetition of this sequence affords, in essentially quantitative yield, 5-silaspiro[4,4]nona-1,6-diene derivatives bearing substituents in the 1,6-positions and 9-borabicyclo[3.3.1]nonyl groups in the 2,7-positions.

Synthesis and Characterization of Spirosilanes – 1,2‐Hydroboration and 1,1‐Carboboration

“…[14] By contrast, the intramolecular 1,1-organoboration proceeds quickly and more smoothly, as studied for vinylsilanes. [7,8,21] The results of the present study lead us to conclude that the consecutive 1,2-hydroboration and 1,1-vinylboration reactions proceed smoothly and selectively independent of the R group. All of the spirosilanes bearing boryl groups at the 2-and 7-positions were colorless oily or crystalline materials, and their structures could be deduced from a consistent set of solution-state NMR spectroscopic data ( Figure 2 and Table 1) and also by X-ray diffraction (Figures 3 and 4).…”

“…The proposed mechanism of the reaction for the synthesis of the spirosilanes given in Scheme 2 has already been discussed in greater detail, [21] supported by theoretical cal-culations. [25] In a first step, silanes bearing vinyl and alkynyl groups at the Si atom react with 9-borabicyclo[3.3.1]nonane (9-BBN) selectively by 1,2-hydroboration of the C=C bond, and the boron atom preferably becomes linked to the terminal carbon atom of the vinyl group (intermediate C, Scheme 2).…”

“…Finally 1,1-vinylboration leads to the spirosilane by twofold ring closure. [21] Usually, the intermolecular 1,1-organoboration of alkynylsilanes with trialkylboranes (BR 3 ) requires harsh conditions and long reaction times. [14] By contrast, the intramolecular 1,1-organoboration proceeds quickly and more smoothly, as studied for vinylsilanes.…”

“…tions appears to be versatile in synthesis. [4][5][6][7][8][9]20,21] In the present work, further examples are given to emphasize the simple and general route to 5-silaspiro [4,4]nona-1,6-diene derivatives. Furthermore, a route to other types of spirosilanes containing the 1-silacyclopent-2-ene unit is explored.…”

Alkynylsilanes and Alkynyl(vinyl)silanes. Synthesis,Molecular Structures and Multinuclear Magnetic Resonance Study

“…We have divided the alkynylsilanes into two classes, those accessible via conventional reactions of commercial chlorosilanes with alkynyllithium or ethynylmagnesium reagents (Scheme 1), and others obtained by more sophisticated stepwise procedures (Scheme 2 -4). Many of these alkynylsilanes have already been used in reactions with dialkylboranes [4,5] combining 1,2-hydroboration with 1,1-organoboration, or with triorganoboranes for 1,1-organoboration [6 -8].…”