Rhodium-catalyzed direct coupling of biaryl pyridine derivatives with internal alkynes

Article abstract of DOI:10.1039/c4cc02822h

Axially chiral biaryls were synthesized by an isoquinoline or 2-pyridine-directed Rh(iii)-catalyzed dual C-H cleavage and coupling with internal alkynes in good to excellent yields. Oxidation of isoquinoline derivatives with m-CPBA furnished their corresponding N-oxides, which could be utilized as Lewis base catalysts in asymmetric reactions. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4cc02822h

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Rhodium-catalyzed direct coupling of biaryl
pyridine derivatives with internal alkynes†
Cite this: Chem. Commun., 2014,
50, 8204
Jun Zheng and Shu-Li You*
Received 16th April 2014,
Accepted 1st June 2014
DOI: 10.1039/c4cc02822h
www.rsc.org/chemcomm
Axially chiral biaryls were synthesized by an isoquinoline or 2- the directing group and chiral auxiliary, the group of Colobert
pyridine-directed Rh(III)-catalyzed dual C–H cleavage and coupling realized the direct atropodiastereoselective C–H olefination of
with internal alkynes in good to excellent yields. Oxidation of biaryl compounds.14 Very recently Yang and co-workers succeeded
isoquinoline derivatives with m-CPBA furnished their corres- in palladium-catalyzed C–H acetoxylation of optically pure
ponding N-oxides, which could be utilized as Lewis base catalysts 2-diphenylphosphine oxide-1,10-binaphthyl, which could lead
in asymmetric reactions.
to the synthesis of (R)-MeO-MOP.15 Despite the above elegant
methods for the construction of atroposelective scaffolds, novel
Axially chiral biaryl units are embedded in many important approaches to build axially chiral biaryls are still highly demanded.
natural products1 and widely applied as chiral auxiliaries,
Usually, increasing the steric hindrance of axially chiral biaryls
ligands and catalysts in asymmetric syntheses.2 The rapidly could have an enormous impact on their performance in asym-
increasing interest in axially chiral biaryls has led to the metric catalysis.16 However, the introduction of arylated naphtha-
development of a great variety of successful methods for their lene and anthracene units to axially chiral biaryl scaffolds is far
atroposelective construction.3 However, the vast majority of from developed. Although numerous methods for construction of
these methods are focused on the synthesis of axially chiral polyarylatedarenes have been developed in the past decades,17
biaryls via Suzuki couplings.4 Some other approaches involve the transition metal-catalyzed C–H bond activation in an aromatic
desymmetrization of prochiral biaryl compounds,5 atroposelec- substrate followed by coupling with alkynes has been considered
tive cleavage of the biaryl lactones with chiral nucleophiles,6 as a particularly useful tool.18 In this regard, Miura, Sato and
asymmetric oxidative coupling of 2-naphthalenol derivatives7 co-workers reported an effective aromatic homologation by
and asymmetric [2+2+2] cycloaddition of an a,o-diyne and Rh(III)-catalyzed oxidative annulations of the phenylazoles and
monoalkynes.8 As an alternative method for atroposelective 2-phenylpyridine with diarylacetylenes.19 Herein, we report the
biaryl synthesis, the functionalization of achiral biaryl com- synthesis of axially chiral biaryl compounds from 2-arylpyridines
pounds via C–H bond cleavage is highly efficient,9 but less or 1-arylisoquinolines and internal alkynes through Rh(III)-
explored. In this context, Murai and co-workers reported the catalyzed dual C–H functionalization/cycloaromatization.
atroposelective alkylation of naphthyl pyridines and naphthyl
Our studies commenced with the reaction between
isoquinolines by a Rh(I)-catalyzed C–H activation reaction.10 1-(naphthalen-1-yl)isoquinoline 1a and diphenyl acetylene 2a
The same group also described a Ru-catalyzed silylation of using [RhCp*Cl2]2 as the catalyst and Cu(OAc)2 as the oxidant
2-(1-naphthyl)-3-methylpyridine in 2003.11 Later Lassaletta and (Table 1). The examination of several silver salts revealed that
co-workers reported Ir(III)-catalyzed nitrogen-directed borylations AgSbF6 is optimal (for detailed studies, see the ESI†). The
of 2-arylpyridines and 1-arylisoquinolines.12 Pd(II)-catalyzed desired product 3a was obtained in 99% yield (entry 1). After
intermolecular C–H phosphorylation of 1-(naphthalen-1-yl)iso- acidification of 3a, the structure of protonated 3a was deter-
quinoline was reported by Yu and co-workers in 2013.13 In mined by single crystal X-ray diffraction analysis (see the ESI†
addition, by taking advantage of a chiral sulfoxide moiety as for details). The presence of 1 equiv. of Cu(OAc)2 was enough
for this reaction, affording 3a in 99% yield (entry 2). Other
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
oxidants such as benzoquinone or oxygen were ineffective
(entries 3 and 4). The choice of solvent was also crucial for this
reaction. The reaction in tert-amyl alcohol gave the best result,
Chemistry, Chinese Academy of Sciences, 345 Lingling Lu, Shanghai 200032, China.
E-mail: slyou@sioc.ac.cn; Fax: +86-21-54925087
† Electronic supplementary information (ESI) available. CCDC 997510 and
in which 3a was obtained in almost quantitative yield. Other
solvents such as ClCH2CH2Cl, toluene, DMA and tBuOH were
997511. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c4cc02822h
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Table 1 Optimization of reaction conditions for biaryl construction via
dual C–H bond cleavagea
Table
2
Rhodium(III) catalyzed cyclization of 2-arylpyridines and 1-
arylisoquinolines (1) with alkynes (2)a
Entry
Solvent
Oxidant
Yieldd (%)
1b
2
t-AmylOH
t-AmylOH
t-AmylOH
t-AmylOH
ClCH2CH2Cl
Toluene
DMA
t-BuOH
t-AmylOH
t-AmylOH
t-AmylOH
t-AmylOH
Cu(OAc)2
Cu(OAc)2
BQ
99
99
Trace
Trace
32
77
79
84
98
3
4g
5
O2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
6
7
8
9c
10h
11e
12f
97
23
NR
a
Unless otherwise noted, all reactions were run in 1 (0.2 mmol),
a
2 (0.44 mmol), [RhCp*Cl2]2 (3.0 mol%), AgSbF6 (15.0 mol%), Cu(OAc)2
(0.2 mmol) and t-amyl alcohol (2 mL) in a sealed tube at 120 1C. Isolated
yields are reported. Reaction was run on a 0.1 mmol scale with
Unless otherwise noted, all reactions were carried out under the
following conditions: [RhCp*Cl2]2 (5 mol%), AgSbF6 (25 mol%), 1a/2a/
Cu(OAc)2 = 1/2.2/1, 0.1 mol Lꢀ1, and t-amyl alcohol (1 mL) in a sealed
b
b
c
5 mol% of [RhCp*Cl2]2.
tube at 120 1C for 12 h. Cu(OAc)2 (2 equiv.) was used. 3 mol%
d
[RhCp*Cl2]2 and 15 mol% AgSbF6 were used. Isolated yield.
e
g
f
1 mol% [RhCp*Cl2]2hand 5 mol% AgSbF6 were used. W/O [RhCp*Cl2]2.
1 atm O2 was used. 2 mmol 1a and 4.1 mmol 2a were used.
yields (Scheme 1). The enantiomers of 4a and 4h were easily
separated by chiral preparative HPLC methods. Fortunately, the
absolute configuration of product (+)-4h was assigned as R by
an X-ray crystallographic analysis of a single crystal of the
enantiopure sample (see the ESI† for details).
The enantiopure N-oxides 4a and 4h were tested in the
asymmetric allylation of benzaldehyde with allyltrichlorosilane,
as shown in Scheme 2. After a preliminary examination, both
N-oxides 4a and 4h could catalyze this reaction but with mode-
rate reactivity and enantioselective control. 1-Phenylbut-3-en-1-ol
was obtained in 29% yield, 62% ee by using (+)-4a and 62% yield,
less effective (32–84% yields, entries 5–8). Finally, reducing the
loading of [RhCp*Cl2]2 from 5 mol% to 3 mol% led to the
isolation of 3a in 98% yield (entry 9). Furthermore, the reaction
on a 2 mmol scale (1a) proceeded smoothly without notable
erosion in yield (97%, entry 10). However, further reducing the
loading of [RhCp*Cl2]2 to 1 mol% resulted in a dramatically
decreased yield (23% yield, entry 11). As expected, no reaction
occurred in the absence of [RhCp*Cl2]2 (entry 12). Thus, the
optimal conditions were identified as the following: 3 mol%
[RhCp*Cl2]2, 15 mol% AgSbF6, 2.2 equiv. of biphenyl acetylene,
1 equiv. of Cu(OAc)2 in tert-amyl alcohol at 120 1C for 12 h, and
under these conditions product 3a was obtained in 98% yield.
Under the optimal reaction conditions described above,
various substituted symmetrical alkynes (2b–f) were treated with
1-(naphthalen-1-yl)isoquinoline 1a and gave the desired polyary-
lated anthracene products (3b–f) in excellent yields (Table 2).
When 1,2-di-p-tolylethyne (2b) was used, 3b was obtained in 77%
yield. Using 5 mol% of [RhCp*Cl2]2, product 3b was obtained
in 93% yield. Unfortunately, when 5-decyne and 1-phenyl-1-
propyne were tested with 1-(naphthalen-1-yl)isoquinoline under
the optimized reaction conditions, only a trace amount of the
desired product was observed in both cases.
Scheme 1 Oxidation of 3a and 3h.
On the other hand, various substituted 2-arylpyridines or
1-arylisoquinolines (1b–f) reacted smoothly with diphenyl acety-
lene 2a to give their corresponding polyarylated naphthalene and
anthracene derivatives (3g–l) in good to excellent yields (Table 2).
The development of novel chiral pyridine N-oxides as Lewis
base catalysts has been one active project in asymmetric
synthesis.20 To test the utility of products obtained here, the
oxidation of 3a and 3h with m-CPBA furnished the desired
pyridine N-oxides 4a and 4h, respectively, in good to excellent
Scheme 2 Application of enantiopure N-oxides 4a and 4h.
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28% ee by using S-(ꢀ)-4h (eqn (1)). These chiral N-oxides also Notes and references
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demonstrated to be suitable organocatalysts. Further applica-
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investigation, and the development of asymmetric reactions are
currently underway in our laboratory.
We thank the National Basic Research Program of China
(973 Program 2010CB833300) and the National Natural Science
Foundation of China (21025209, 21121062, and 21332009) for
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