Efficient synthesis of dibenzoxaborininols from diaryl ethers and their application to dibenzofuran synthesis

Article abstract of DOI:10.1002/adsc.201300567

A convenient and efficient method for the borylation of diaryl ethers leading to dibenzoxaborininols and the synthesis of dibenzofuran derivatives has been developed. The borylation involves the sequential three-step process: lithiation, borylation and hydrolysis. The synthesized dibenzoxaborininols could be readily transformed into dibenzofuran derivatives in good to excellent yields under palladium catalysis in the presence of iodine, and this is the first example for the formation of an aryl C-C bond from diarylborinic acids. Copyright

Full text of DOI:10.1002/adsc.201300567

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DOI: 10.1002/adsc.201300567
Efficient Synthesis of Dibenzoxaborininols from Diaryl Ethers
and Their Application to Dibenzofuran Synthesis
Liting Niu,a Haijun Yang,a Yuyang Jiang,b and Hua Fua,b,*
a
Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology (Ministry of Education), Department of
Chemistry, Tsinghua University, Beijing 100084, Peopleꢀs Republic of China
Fax : (+86)-10-6278-1695; e-mail: fuhua@mail.tsinghua.edu.cn
Key Laboratory of Chemical Biology (Guangdong Province), Graduate School of Shenzhen, Tsinghua University,
b
Shenzhen 518057, Peopleꢀs Republic of China
Received: June 26, 2013; Revised: October 12, 2013; Published online: December 11, 2013
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201300567.
Abstract: A convenient and efficient method for the rivatives in good to excellent yields under palladium
borylation of diaryl ethers leading to dibenzoxabori- catalysis in the presence of iodine, and this is the
À
ninols and the synthesis of dibenzofuran derivatives first example for the formation of an aryl C C bond
has been developed. The borylation involves the se- from diarylborinic acids.
quential three-step process: lithiation, borylation and
À
hydrolysis. The synthesized dibenzoxaborininols Keywords: borylation; C H functionalization; diben-
could be readily transformed into dibenzofuran de- zofurans; palladium; Suzuki coupling
Introduction
action conditions including the strong bases, additives,
solvents, boronic acid esters, ratio of agents and tem-
Arylboronic acids are important building blocks in or- perature. The experimental results showed that the
ganic synthesis because of their non-toxicity, air- and optimum conditions for the borylation of diaryl ethers
moisture-stability, and tolerance of functional (1) were as follows: 3 equiv. of LiBu-n as the base,
groups,[1] and their application in the transition metal- 3 equiv. of N,N,N’,N’-tetramethylethylenediamine
catalyzed formation of carbon-carbon and carbon-het- (TMEDA) as the additive, anhydrous THF as the sol-
eroatom bonds makes them one of the most useful vent at À788C to room temperature for the first step;
building blocks in both academic laboratories and in- 3 equiv. of BACTHNURGTNEUNG(OMe)3 as the borylating agent at room
dustry.[1b,2] However, the use of diarylborinic acids and temperature for the second step; and saturated aque-
triarylboranes is still in its infancy.[3] To the best of ous NH4Cl as the quenching and hydrolytic agent for
our knowledge, the only example for the synthesis of the third step (see Table 1). With these optimized
dibenzoxaborininol was reported via the reaction of conditions in hand, we investigated the substrate
(2-LiC6H4)2O with tributyl borate, and a low yield scope of this borylation reaction. As shown in
(18%) was provided.[4] Unfortunately, the application Table 1, the examined substrates provided good yields
of dibenzoxaborininol in organic synthesis is not de- for the sequential three-step process: lithiation, bory-
veloped thus far. On the other hand, dibenzofuran de- lation and hydrolysis. For diaryl ethers with ortho- or
rivatives widely occur in natural products and biologi- para-site substituted groups, the borylation provided
cally active molecules,[5] and their synthesis has at- only one product. For the substrates containing naph-
tracted much attention.[6] Herein, we report a simple, thalene (entries 8, 14 and 22), two isomers were ob-
convenient and highly efficient approach to dibenz- served, but b-borylation was the primary reaction. 1-
ACHTUNGTRENNUNGoxaborininol and dibenzofuran derivatives using (m-Tolyloxy)benzene (1c) also provided two bisbory-
diaryl ethers as the starting materials.
lation products (entry 3). Borylation of 1-methoxy-3-
phenoxybenzene derivatives (1g, 1l, 1p, 1s, 1u and 1v)
selectively occurred at the 2-site carbon between
MeO and ArO groups because of the extra coordina-
tion of lithium with the meta-methoxy group during
Results and Discussion
First, borylation of 1-methyl-4-phenoxybenzene (1b) the lithiation process (entries 7, 12, 16, 19, 21 and 22).
was chosen as the model substrate to optimize the re-
Adv. Synth. Catal. 2013, 355, 3625 – 3632
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Liting Niu et al.
Table 1. One-pot borylation of diaryl ethers (1) with BACTHNUTRGNEUNG
(OMe)3 leading to dibenzoxaborininols.[a]
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Efficient Synthesis of Dibenzoxaborininols from Diaryl Ethers
Table 1. (Continued)
Adv. Synth. Catal. 2013, 355, 3625 – 3632
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Liting Niu et al.
Table 1. (Continued)
[a]
Reaction conditions: diaryl ether (1) (1 mmol), LiBu-n (3 mmol), BACHTNUTRGNEUNG(OMe)3 (3 mmol), TMDEA
(3 mmol), THF (4 mL) under a nitrogen atmosphere for the first and second steps.
Isolated yield (total yield from 1 to 3).
[b]
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ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2013, 355, 3625 – 3632