40965-54-6Relevant articles and documents
Hydroboration. 56. Convenient and Regiospecific Route to Functionalized Organosilanes through the Hydroboration of Alkenylsilanes.
Soderquist, John A.,Brown, Herbert C.
, p. 3571 - 3578 (1980)
A systematic and detailed study of the hydroboration of several representative alkenylsilanes is reported.By use of a 1:1 molar stoichiometry, the hydroboration of vinyltrimethylsilane (1) at 0 deg C with BH3*THF gives a mixture of dialkylborane products exclusively with a ca. 60:40 distribution of a α- and β-silylethyl groups in these adducts.Redistribution of the reaction mixture at a somewhat higher temperature (50 deg C) gives the corresponding monoalkylboranes.The redistribution process is regiospecific, leaving the original 60:40 ratio of α- and β-silylethyl groups in the dialkylboranes unchanged in the monoalkylboranes produced.With a 3:1 ratio of 1 to BH3*THF, equimolar amounts of dialkyl- and trialkylborane products are formed in the hydroboration reaction.Under these conditions, the α to β ratio changes modestly to 50:50.The failure of the hydroboration to attain complete conversion to the trialkylborane stage is attributed largely to the low reactivity of meso-bisborane produced in the reaction in the further hydroboration of 1.The change in the regioselectivity from 60:40 to 50:50 with a 3:1 stoichiometry is attributed to the higher β selectivity of dialkylboranes in the hydroborationof 1.Thus, the hydroboration of 1 with 9-borabicyclononane (9-BBN) is regiospecific, giving exclusively the B--9-borabicyclononane (3) product.Redistribution of 3 with BH3*THF gives essentially complete conversion to 9-BBN and pure bisborane.This compound hydroborates 1 rapidly at 0 deg C, giving predominantly (ca. 85percent) the β adduct, trisborane.Hydroboration of propen-2-yltrimethylsilane with BH3*THF gives primarily (91percent) β boron placement.However, use of 9-BBN eliminates the formation of the minor internal product and gives (2-Me3Si-1-Pr)-9-BBN exclusively.Hydroboration of cis-1-propenyltrimethylsilane (17) with BH3*THF proceeds to the dialkylborane stage, with no significant formation of the corresponding trialkylborane.The hydroboration is highly regioselective, giving the bisborane product in 95percent regioisomeric purity.This borane is unusual in that it is monomeric in solution, as revealed by IR and 11B NMR data.Hydroboration of 17 with 9-BBN is much less selective than that with BH3*THF, a rare occurrence, giving essentially equal amounts of regioisomeric adducts.Hydroboration of allyltrimethylsilane with either BH3*THF or 9-BBN gives the (γ-silylpropyl)borane product exclusively.Hydroboration of 3-buten-1-yltrimethylsilane with BH3*THF gives the (δ-silylbutyl)borane adduct in 94percent isomeric purity.With 9-BBN, the hydroboration is regiospecific, giving the (δ-silylbutyl)borane adduct exclusively.Thus, through hydroboration, the syntheses of α, β, γ, and δ boron-functionalized organosilanes are achieved, making such compounds available for use as synthetic intermediates.The 13C and 11B spectra...
