DOI: 10.1002/chem.201500816
Communication
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Asymmetric Catalysis |Hot Paper|
Palladium/Zinc Co-Catalyzed syn-Stereoselectively Asymmetric
Ring-Opening Reaction of Oxabenzonorbornadienes with Phenols
[
b]
[a]
[a, d]
[a]
[a]
[c]
Sifeng Li, Jianbin Xu, Baomin Fan,*
Zhiwu Lu, Chaoyuan Zeng, Zhaoxiang Bian,
[a]
[b]
Yongyun Zhou, and Jun Wang*
[
6b,12]
ners by choosing different metal catalysts, such as Rh,
Abstract: A new palladium/zinc co-catalyst system associ-
ated with chiral (R)-Difluorphos for asymmetric ring-open-
ing reaction of oxabenzonorbornadienes with phenols is
reported. This catalyst system allows the formation of cis-
[2e,3a,b]
[2a,b,f,6c,13]
[14]
[15]
Cu,
Pd,
Pt and Ni. Yet, for the ring-opening
addition of oxabenzonorbornadienes with oxygen- or nitro-
gen-based nucleophiles, only trans-configuration products
[7,8,10,11,16]
were generally observed with Rh, Ir or Ru catalysts.
To
2
-aryloxy-1,2-dihydronaphthalen-1-ol products in good
yields (up to 95% yield) with excellent enantioselectivities
up to 99% ee). The cis-configuration of the product has
the best of our knowledge, there has been no example in ring-
opening reaction of oxabenzonorbornadienes with heteroatom
nucleophiles to afford cis-2-aryloxy-1,2-dihydronaphthalen-1-ol.
In fact, they are important scaffolds for total synthesis of many
(
been confirmed by X-ray crystal structure analysis. To the
best of our knowledge, it represents the first example in
ring-opening reactions of bicycloalkenes with heteronu-
cleophiles in a syn-stereoselective manner.
[17]
bioactive compounds.
Recent literatures showed that cis-2-aryloxy-1,2-dihydro-
naphthalen-1-ols could be accessed by cross-coupling of cis-
1
,2-dihydronaphthalen-1,2-diol with ArBF K in the presence of
3
[18]
copper(II) acetate. The parent cis-1,2-dihydronaphthalen-1,2-
Transition metal-catalyzed asymmetric ring-opening (ARO) re-
actions of oxabenzonorbornadienes have attracted continuous
interest and extensive study due to their advantages of
straightforward access to chiral hydronaphthalenes, in which
they are widely exist as the subunit in natural products and
diol could be afforded by bacterial oxidation of aromatic mole-
[19]
cules
or by multi-step synthesis from ortho-vinylbenzalde-
[20]
hyde.
Indeed, a general and stereocontrolled method for
easy access of cis-dihydronaphthalen-1,2-diols with various
substituents is still in demand. In this regard, the ARO pathway
leading to cis-2-aryloxy-1,2-dihydronaphthalen-1-ol products in
one step would be a desirable approach.
[
1]
bioactive molecules. Considerable progresses have been
made for this type of reactions since Lautens’s initial work.
With the aid of various chiral transition-metal cata-
[
2–6]
lysts, a variety of carbo-
and heteroatom nucleo-
[
7–11]
philes
reacted with oxabenzonorbornadienes
successfully leading to substituted hydroxyl-dihydro-
naphthalenes. In the ring-opening addition of car-
bonucleophiles to oxabenzonorbornadienes, both cis
and trans configured products can be obtained in
a highly diastereoselective and enantioselective man-
Scheme 1. Asymmetric ring-opening reaction of oxabenzonorbornadienes with O- or N-
based nucleophiles.
In continuing our research interest of ring-opening reaction
+
[
a] J. Xu, Prof. B. Fan, Z. Lu, C. Zeng, Y. Zhou
[21,22]
using carbonucleophiles,
herein we report a transition
YMU-HKBU Joint Laboratory of Traditional Natural Medicine
Yunnan Minzu University, Kunming 650500 (P. R. China)
E-mail: adams.bmf@hotmail.com
metal/Lewis acid co-catalyst system for asymmetric ring-open-
ing reaction of oxabenzonorbornadienes with phenolic or
naphtholic nucleophiles. Remarkably, this method gave exclu-
sive syn-selective outcome the first time, in which it is comple-
mentary to previous methods for trans-configuration product
formation (Scheme 1).
+
[
b] S. Li, Prof. J. Wang
Department of Chemistry
South University of Science and Technology of China
Shenzhen, Guangdong, 518055 (P. R. China)
E-mail: wang.j@sustc.edu.cn
[
c] Prof. Z. Bian
School of Chinese Medicine
Hong Kong Baptist University
We embarked this investigation using oxabenzonorborna-
diene 1a and phenol 2a as benchmark substrates with
Pd(OAc) catalyst and Lewis acid Zn(OTf) as co-catalyst in com-
2
2
[d] Prof. B. Fan
bination with a range of chiral diphosphine ligands (Table 1).
Gratifyingly, commercially available ligand (R)-Binap gave cis-2-
phyloxy-1,2-dihydronaphthalen-1-ol 3aa in 66% yield with
State Key Laboratory of Elemento-organic Chemistry
Nankai University, Tinajim, 300071 (P. R. China)
+
[
] These authors contributed equally to this work.
7
6% ee in DCE at room temperature for 12 h (Table 1, entry 1).
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201500816.
The best product enantioselectivity was obtained by employ-
Chem. Eur. J. 2015, 21, 1 – 6
1
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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