Abstract
Hydroboration is an emerging method for mild and selective reduction of carbonyl compounds. Typically, transition‐metal or reactive main‐group hydride catalysts are used in conjunction with a mild reductant such as pinacolborane. The reactivity of the main‐group catalysts is a consequence of the nucleophilicity of their hydride ligands. Silicon hydrides are significantly less reactive and are therefore not efficient hydroboration catalysts. Here, a readily prepared silyl anion is reported to be an effective initiator for the reduction of aldehydes and ketones requiring mild conditions, low catalyst loadings and with a good substrate scope. The silyl anion it is shown to activate HBpin to generate a reactive borohydride in situ which reacts with aldehydes and ketones to afford the hydroboration product.
Highlights
All manipulations were carried out under a dry argon or nitrogen atmosphere using standard Schlenk or glovebox techniques
Solvents were obtained from an Inert solvent purification system and stored over 4 Å molecular sieves
C6D6 was dried over potassium distilled under argon and stored over 4 Å molecular sieves
Summary
All manipulations were carried out under a dry argon or nitrogen atmosphere using standard Schlenk or glovebox techniques. Solvents were obtained from an Inert solvent purification system and stored over 4 Å molecular sieves. C6D6 was dried over potassium distilled under argon and stored over 4 Å molecular sieves. 1H and 13C NMR spectra were recorded on Bruker AVA 400, 500 or 600 MHz spectrometers. 11B NMR spectra were recorded on a Bruker PRO 500 spectrometer. 1H and 13C spectra were referenced to residual solvent signals.[1] 11B spectra were referenced to BF3·Et2O as an external standard. Pinacolborane (HBpin) was distilled prior to use to remove traces of BH3, boric acid and B2pin which was confirmed by 1H and 11B NMR. Acetophenone was stored over 4 Å molecular sieves. All other reagents were used as supplied. Catalysts 1,[2] A[3] and B[4] were prepared according to literature procedures
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