10.1002/chem.202000897
Chemistry - A European Journal
COMMUNICATION
We carried out a series of stoichiometric reactions to support the
proposed mechanism. Initially, we investigated the stoichiometric
reaction of silyl anion 1 with HBpin in C6D6 and THF-d8. In each
case, a gel-like solid formed immediately. The 11B NMR of the
C6D6 reaction mixture shows a single broad singlet resonance at
Keywords: Hydroboration • Silyl anion • Carbonyl • Reduction •
Silicon
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δ 37.4 (ν = 230 Hz) which corresponds to silylboronic ester 3.[8]
½
In THF-d8, besides the signal for 3 at δ 37.4, a sharp singlet at δ
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Scheme 4. BH3·THF is not an effective catalyst for the hydroboration of
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It has recently been reported that BH3·THF can catalyze the
hydroboration of alkenes and alkynes.[10] To rule out silyl-anion
induced decomposition of HBpin to BH3, which could act as a
catalyst, we carried out a test reaction using 1 mol% BH3·THF
with acetophenone and one equivalent of HBpin under otherwise
identical reaction conditions. After one hour at room temperature
we only observed trace amounts of the hydroboration product 2a,
demonstrating that BH3 is not an efficient catalyst under our
conditions. This observation is particularly important given the
observation of a BH3 adduct in the reaction of 1 with HBpin
described above. Furthermore, the hydroboration of alkynes did
not proceed at room temperature under identical conditions (see
supporting information).
In conclusion, we have presented a fast, reliable and facile
method for the hydroboration of carbonyls using a silyl anion
initiator. We have carried out a substrate scope investigation
which shows the reaction is tolerant to a range of substituents.
Our proposed mechanism is supported by previously reported
protocols and stoichiometric studies.
Acknowledgements
MJC, and AB acknowledge funding from the EPSRC for the
CRITICAT CDT (EP/L016419/1). MWS thanks the Carnegie Trust for
the award of a PhD Scholarship. The authors would like to thank
Dr Stephen Thomas for helpful discussions during the course of
this work.
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