DOI: 10.1002/chem.201001943
À
Borylation of Aryl and Alkenyl Carbamates through Ni-Catalyzed C O
Activation
Kun Huang,[a] Da-Gang Yu,[a] Shu-Fang Zheng,[a, b] Zhen-Hua Wu,[a] and
Zhang-Jie Shi*[a, b]
In the past several decades, Suzuki–Miyaura coupling has
been well developed and has become one of the most useful
reported Ni-catalyzed borylation starting from aryl mesy-
lates and tosylates.[4i] Based on our and othersꢀ recent inves-
À
À
tools to construct C C bond in both laboratory and indus-
tigations on the cleavage of aryl C O bond of aryl carbox
A
G
try.[1] As the major coupling partner of Suzuki–Miyaura cou-
pling, aryl boronic acid and its derivatives showed their ad-
vantages due to the readily availability, low toxicity and
high functional group tolerance.[2] Traditionally, they can be
prepared by metal exchange from aryl Grignard reagents or
aryl lithium reagents with boronic esters, in which the sensi-
tivity to moisture and functional group incompatibility limits
their implementation.[3] Subsequently, new methods were
developed through direct borylation starting from aryl ha-
ates and other derivatives,[2f,9] we envisioned that it might be
possible to carry out aryl borylation from arylcarbox
by means of Ni catalysis (Scheme 1).
ACHTUNGTRENNUNGylACHTUNGTRENNUNGates
ACHTUNGTRENNUNGlides, catalyzed by Pd and other metal complexes and avoid-
ing the use of aryl metallic reagents.[4] Recent advances also
Scheme 1. Rational design of the borylation of phenol derivatives.
À
showed the power of the direct C H borylation with Rh
and Ir catalysis.[5] Herein we reported a novel useful method
to produce aryl boronic esters from aryl and vinyl carba-
mates with diboronic reagents through Ni catalysis.
With this idea in mind, we started searching for the best
procedure to approach our goal. Based on the recent stud-
ies, we found that 2-naphthyl N,N-dimethylcarbamate (1aa)
showed the excellent reactivity in both Suzuki–Miyaura and
Kumada couplings.[10] Gargꢀs and Snieckusꢀ studies also
made significant contributions to present the similar re-
sults.[11] Thus, the carbamate 1aa was first selected as a stan-
dard substrate for the reaction condition screening
(Table 1). To our satisfaction, when carbamate 1aa and neo-
pentylglycolborylate 2a[12] were reacted in dioxane in the
Phenols and carbonyl compounds exist in many forms in
the natural and synthetic world.[6] However, only very few
examples for the construction of useful aryl boronic deriva-
tives starting from phenol and ketone compounds have been
reported.[4g,7] In some examples, aryl sulfonates have been
successfully applied to carry out the borACHTNUTRGENNUGylCAHUTGTNRENNUG
ation.[8] When we
were preparing this manuscript, Percec and co-workers first
presence of [NiACHTUNGTRNEG(UN PCy3)2Cl2] (10 mol%; Cy=cyclohexyl) and
[a] Dr. K. Huang, D.-G. Yu, S.-F. Zheng, Z.-H. Wu, Prof. Z.-J. Shi
Beijing National Laboratory of Molecular Sciences (BNLMS)
PKU Green Chemistry Centre and
additional PCy3 (20 mol%) as catalyst and NaOtBu as base,
the desired borylation product 3a was obtained in 21% iso-
lated yield. The solvent is very critical for this transforma-
tion. When toluene was applied as solvent, the yield was en-
hanced to 46%, while dimethoxylethane (DME) completely
inhibited the transformation. To our surprise, the mixture of
toluene/DME with 1:1 ratio was beneficial for this transfor-
mation and the isolated yield was up to 81% in the presence
of 5.0 mol% of Ni catalyst (entry 6, Table 1). Decreasing the
amount of 2a led to lower yield. On the other hand, the
amount of base (NaOtBu) was also critical. Either increase
Key Laboratory of Bioorganic Chemistry and Molecular Engineering
of Ministry of Education, College of Chemistry
Peking University, Beijing 100871 (P.R. China)
[b] S.-F. Zheng, Prof. Z.-J. Shi
State Key Laboratory of Organometallic Chemistry
Chinese Academy of Sciences, Shanghai 200032 (P.R. China)
and
College of Chemistry and Material Sciences
Sichuan Normal University, Chengdu, Sichuan 610068 (P.R. China)
Fax : (+86)10-6276-0890
786
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 786 – 791