10.1002/anie.202007352
Angewandte Chemie International Edition
COMMUNICATION
Acknowledgements
We are grateful for financial support from the National Natural
Science Foundation of China (21871147, 91956106, and
21602114) and the Fundamental Research Funds for Central
Universities (2122018165). X.-C.W. thanks the Tencent
Foundation for support via the Xplorer Prize.
Keywords: boron • asymmetric catalysis • pyridine • reduction •
heterocycles
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Scheme 2. Gram-scale reactions and transformations of products.
To demonstrate the strength of our method, we performed
a gram-scale reaction of S1 in the presence of only 0.5 mol %
of 1a. The reaction afforded piperidine P1 in 89% yield with
90% ee (Scheme 2a), and almost all of the proton donor could
be recovered after hydrolysis of the 3,5-(CF3)2C6H3NAc(Bpin)
generated as
a
byproduct. We then carried out
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rearrangement
in
the
presence
of
lithium
bis(trimethylsilyl)amide gave ring-expansion product 3[24] in
good yield and good diastereoselectivity with 89% ee. These
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rapid access to enantioenriched olefin-containing bicyclic
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an intermediate in
a previously reported synthesis of
caulophyllumine B[17] (Scheme 2b).
In conclusion, we have developed a method for metal-free
enantioselective reduction of 2-vinylpyridines with catalysis by
chiral spiro-bicyclic bisboranes. The reaction is the first
example of a metal-free borane-catalyzed enantioselective
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