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Scheme 5 A gram-scale borylation reaction.
Scheme 2 Suzuki–Miyaura cross-coupling of b-hydroxyl boronic ester
with arylhalides.
Our method presents a straightforward catalytic method for
the preparation of b-hydroxyl boronic esters, which have the
potential for further transformations in organic syntheses.
Moreover, the versatility of the b-hydroxyl boronic ester products
toward the synthesis of the corresponding aryl-substituted alcohols
is underlined. The amination reaction of b-hydroxyl boronic ester
is also described. Expanding of the scope of epoxides, as well as
the investigation of the mechanism for this reaction, is currently
underway in our lab.
We thank the support from the NSFC (21302178, 21325208,
21361140372, 21572212, and 21502184), FANEDD (201424),
FRFCU, PCSIRT, Youth Innovation Promotion Association of
the Chinese Academy of Sciences (2015371), and the CAS-TWAS
President’s Fellowship for International PhD Students.
and aryl bromide were suitable substrates for this C(sp2)–C(sp3)
cross-coupling (as illustrated in Scheme 2).
Several experiments were carried out to confirm the optical
purity of our products. For instance, the obtained products of
b-hydroxyl boronic esters (3bb) of (S)-2-((benzyloxy)methyl)
oxirane can be converted to 1,2-diols (3bd) in 80% yield under
basic conditions with H2O2 (Scheme 3).5 In addition, the
arylation reaction was also conducted for borylated alcohol
(3bd) to give 5b in 57% yield in a stereospecific manner (see
the ESI† for details of HPLC).
We also tested the transformation of our products in
Chan–Evans–Lam cross–coupling reactions.11 A catalytic amount
of Cu(OAc)2 was employed to promote the amination reaction
of b-hydroxyl boronic ester with N-methylaniline. We found that
3a was converted to the corresponding phenyl-amino alcohol
derivative (6a) in 49% yield (Scheme 4).
Notes and references
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To evaluate the efficiency of this novel synthetic strategy
(as copper-catalyzed borylative opening of epoxides), a gram-
scale reaction of 2-(phenylmethyl)oxirane (1a) with B2pin2 was
carried out, and the corresponding product 3a was given in
85% isolated yield (Scheme 5).
In summary, we reported the first copper-catalyzed ring opening
C–B forming reaction of epoxides with diboron reagents.
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(b) P. Crotti and M. Pineschi, Aziridines and Epoxides in Organic
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Scheme 3 Copper-catalyzed borylation reaction of racemic and
chiral epoxides, and palladium-catalyzed arylation reaction of b-hydroxyl
boronic esters.
Scheme 4 Chan–Lam C–N cross-coupling of b-hydroxyl boronic ester
with N-methylaniline.
´
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