The hydroboration of silylacetylenes. The silyl-Markovnikov hydroboration route to pure (Z)-1-(2-borylvinyl)silanes and. beta. -keto silanes
- Univ. of Puerto Rico, Rio Piedras (Puerto Rico)
The regiochemistry and stoichiometry of the hydroboration of simple 1-silylacetylenes with 9-borabicyclo(3.3.1)nonane (9-BBN) was examined in detail. (Trimethylsilyl)acetylene (1c) results in only {beta}-mono- and dihydroboration products, behavior common to nonsilylated terminal acetylenes. It is less reactive than its alkyl counterparts toward 9-BBN. it was also demonstrated that (1-trimethylsilyl)alkynes form ({alpha}-borylvinyl)silanes, similar to 1-alkynes, but they are much less reactive. Clean monohydroboration of these silylacetylenes is achieved only with a bulk (e.g. t-Bu) group at the C-2 position. However, compared to 1-alkynes, their dihydrobration products differ markedly, with the former giving 1,2-diboryl compounds, while the latter results in 1,1-diboryl adducts. (Triethyl- and tert-butyldimethylsilyl)propynes exhibit similar reactivity to that of the analogous trimethylsilyl derivative. The triisopropylsilyl group was found to not only completely suppress dihydroboration but also gave exclusively (Z)-({beta}-borylvinyl)silane adducts (9{beta}). Oxidation of 9{beta} produces the corresponding {beta}-keto silanes (12) in excellent yields (i.e. 83-90%). The bulky (triethyl- and tert-butyldimethylsilyl)propyne hydroboration products were found to be thermally unstable with the initially formed ({alpha}-borylvinyl)silanes isomerizing to {alpha}/{beta} mixtures through their 1,2-diboryl diadducts (10). Heating 10 produces (3,3-diborylpropyl)silanes (14). Oxidation of the triethylsilyl compound 14b affords the corresponding {gamma}-silylpropanol (15b). The complete characterization of the intermediate organoboranes by 75-MHz {sup 13}C NMR was achieved. A detailed discussion of the phenomena involved is presented. The observed results are attributed primarily to the additional steric effects imposed on an unsaturated system by a trialkylsilyl group when compared to a hydrogen atom at that position.
- OSTI ID:
- 7072453
- Journal Information:
- Journal of the American Chemical Society; (USA), Journal Name: Journal of the American Chemical Society; (USA) Vol. 111:13; ISSN 0002-7863; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400000* -- Chemistry
400201 -- Chemical & Physicochemical Properties
ACETYLENE
ALKYNES
BORATES
BORON COMPOUNDS
CHEMICAL REACTIONS
DATA
DATA ANALYSIS
EXPERIMENTAL DATA
HYDRIDES
HYDROCARBONS
HYDROGEN COMPOUNDS
HYDROGENATION
INFORMATION
MEASURING INSTRUMENTS
MEASURING METHODS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC SILICON COMPOUNDS
OXYGEN COMPOUNDS
SILANES
SILICON COMPOUNDS
SYNTHESIS