Palladium-catalyzed oxidative C-C bond cleavage cyclization of biaryl-2-amines with alkenes involving C-H olefination and carboamination

Article abstract of DOI:10.1002/adsc.201100651

A new, general method for the synthesis of phenanthridines has been developed by palladium-catalyzed oxidative remote C-H olefination- carboamination-C-C bond cleavage tandem reaction. It is noteworthy that alkenes are used as the one-carbon resources for this tandem reaction. Copyright

Full text of DOI:10.1002/adsc.201100651

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DOI: 10.1002/adsc.201100651
À
Palladium-Catalyzed Oxidative C C Bond Cleavage Cyclization
À
of Biaryl-2-amines with Alkenes Involving C H Olefination and
Carboamination
Yan-Yun Liu,a,b Ren-Jie Song,a Cui-Yan Wu,a,b Lu-Bin Gong,a,b Ming Hu,a,b
Zhi-Qiang Wang,a,b Ye-Xiang Xie,a and Jin-Heng Lia,*
a
State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan
University, Changsha 410082, Peopleꢀs Republic of China
Fax : (+86)-731-8887-2531; phone: (+86)-731-8887-2531; e-mail: jhli@hnu.edu.cn
Key Laboratory of Chemical Biology & Traditional Chinese Medicine Research (Ministry of Education), Hunan Normal
b
University, Changsha 410081, Peopleꢀs Republic of China
Received: August 16, 2011; Revised: November 3, 2011; Published online: January 20, 2012
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201100651.
[5–7]
À
Abstract: A new, general method for the synthesis
of phenanthridines has been developed by palladi-
C H olefination more fascinating.
Diamond and
co-workers have first reported the formation of both
2-methylquinoline and N-ethylaniline from the reac-
tion of aniline with ethylene and PdCl2 at 2008C.[5a]
Subsequently, Miura and co-workers have developed
a mild method for the cyclization of aryl sulfonamides
À
um-catalyzed oxidative remote C H olefination–
carboamination–C C bond cleavage tandem reac-
À
tion. It is noteworthy that alkenes are used as the
one-carbon resources for this tandem reaction.
À
or aryl acids with alkenes via the C H olefination
À
Keywords: alkenes; biaryl-2-amines; oxidative C C
bond cleavage; palladium; phenanthridines
using the Pd
(OAc)2/Cu
(OAc)2/air/base system leading
to the corresponding 5,6-dihydrophenanthridines,
phthalides or isocoumarins (Scheme 1).[6] Since then,
other groups, such as those of Booker-Milburn and
Lloyd-Jones,[5b] Yu,[5c,7a] Zhu[5d] or Kitamura,[7c] have
used this strategy to construct other nitrogen- or
The Heck-type reaction is one of the most important oxygen-containing heterocycles on the basis of the di-
methods for the construction of carbon-carbon bonds recting groups through two pathways: (a) protona-
leading to new alkenes.[1] Generally, halides (aryl or tion[5,6,7b,c] or (b) b-elimination (Scheme 1).[7a] Here,
alkyl halides) are employed for the reaction with al- we report a new, unexpected route for the synthesis
À
À
kenes via the C halogen bond functionalization. Al- of phenanthridines via Pd(II)-catalyzed C C bond
though many catalytic systems have been developed cleavage cyclization of biaryl-2-amines with alkenes
À
for the Heck-type reaction, the associated shortcom- involving remote aryl C H olefination and carboami-
ings are noticeable, as it involves the use of expensive nation (Scheme 1). Importantly, it is the first example
halides and ligands, associated with unnecessary eco- of the C H olefination methodology involving a C C
nomic wastes and environmental pollution. To over- bond cleavage process. It is noteworthy that phenan-
come these drawbacks, a strategy including C H ole- thridines are important units in numerous biologically
À
À
À
fination, initially studied by Fujiwara and Moritani, is active natural products and medicinally significant
an attractive alternative.[2–7] Among the C H olefina- compounds.[8]
À
tion methods, considerable efforts were devoted to
We initiated our study by examining the reaction of
the directing group strategy using Pd(II)/[O] catalytic N-(biphenyl-2-yl)-4-methylbenzenesulfonamide (1a)
system recently because it could improve the reactivi- with butyl acrylate (2a), PdCl2 and Cu(OAc)2 in
AHCTUNGTRENNUNG
ty, extend substrate compatibility and control selectiv- DMA (N,N-dimethylacetamide) at 1208C under an
ity.[3–7] However, examples of the C H olefination, O2 atmosphere, providing phenanthridine 3 in 53%
À
followed by cyclization with directing groups are yield with 70% conversion of 1a (entry 1 in Table 1).[9]
much less abundant.[4–7] Actually, this C H olefination Notably, no Miura product was observed in the reac-
À
and cyclization strategy is useful for the synthesis of tion. This prompted us to investigate other Pd cata-
complicated heterocycles, which makes the directed lysts, including PdACHTUNGTRNENG(U OAc)2, PdCl2ACHTUNTGERN(NUGN MeCN)2, PdI2,
Adv. Synth. Catal. 2012, 354, 347 – 353
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Scheme 1. The C H olefination and cyclization routes.
Table 1. Palladium-catalyzed reaction between N-(biphenyl-2-yl)-4-methylbenzenesulfonamide (1a) and butyl acrylate (2a).[a]
Entry
[Pd] (mol%)
PdCl2 (10)
[O]
Cu(OAc)2
Solvent
Temperature [oC]
Conversion [%][b]
Yield [%][c]
1
2
3
4
G
DMA
DMA
DMA
DMA
DMA
DMA
DMF
120
120
120
120
120
120
120
120
120
120
140
140
140
140
140
140
70
45
38
45
20
60
62
80
46
<5
96
100
100
10
53
25
29
25
15
0
48
50
33
trace
60
64
65
8
Pd
N
Cu(OAc)2
CuCl2
Cu(OTf)2
AgOAc
PhI(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
R
PdCl2 (10)
PdCl2 (10)
PdCl2 (10)
PdCl2 (10)
PdCl2 (10)
PdCl2 (10)
PdCl2 (10)
PdCl2 (10)
PdCl2 (10)
PdCl2 (10)
PdCl2 (10)
PdCl2 (10)
PdCl2 (10)
PdCl2 (5)
E
5
6[d]
7
R
G
T
R
U
AHCTUNGTRENNUNG
R
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
8
9
NMP
DMSO
toluene
DMA
DMA
DMA
DMA
DMA
DMA
10
11
12[e]
13[f]
14[e,g]
15[e,h]
16[e]
T
A
28
100
24
67
[a]
Reaction conditions: 1a (0.3 mmol), 2a (1.5 equiv.), [Pd], [O] (1.5 equiv.)/gas (1 atm) and solvent (3.0 mL) under an O2 at-
mosphere for 48 h.
[b]
The conversion was determined by GC-MS analysis using nitrobenzene as the internal standard. No Miura product was
observed.
Isolated yield.
[c]
[d]
[e]
[f]
À
Another C H amination product, 9-tosyl-9H-carbazole (3A), was obtained in 55% yield.
2a (3.0 equiv.).
2a (4.0 equiv.).
Under an argon atmosphere.
[g]
[h]
Under an air atmosphere.
PdACHTUNGTRENNUNG(dba)2 and PdACHTNUGTRENNUNG
(entry 2 and Table S1 in Supporting Information);[9] Cu
N
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
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Palladium-Catalyzed Oxidative C C Bond Cleavage Cyclization of Biaryl-2-amines with Alkenes
Table 2. Screening of the directing groups.[a]
[a]
Reaction conditions: 1 (0.3 mmol), 2a (3 equiv.), PdCl2 (5 mol%),
CuACHTUNTRGNEUNG(OAc)2 (1.5 equiv.) and DMA (3 mL) at 1408C under an O2 atmos-
phere for 48 h.
AgOAc displayed less efficiency (entries 3–5). Sur- thy that the reaction activity is decreased under either
prisingly, PhIACHTUNGTRENNUNG(OAc)2 has no effect on the reaction, but air or argon atmosphere in terms of yield (entries 14
À
prompted the C H bond activation/amination reac- and 15). Gratifyingly, satisfactory results were still
tion (entry 6).[10] We found that both DMF and NMP achieved at a loading of 5 mol% PdCl2 (entry 16).
were also suitable media for the reaction, but DMSO
and toluene lowered the activity (entries 7–10). To riety of amino-directing groups, including NHTs,
our delight, the yield of 3 was enhanced to 60% by in- NHBn, NHMe, NH(allyl), NHBoc, NH(CHO),
With the optimal reaction conditions in hand, a va-
A
ACHTUNGTRENNUNG
creasing the reaction temperature (entry 11). Screen- NHAc and NH2, were explored (Table 2). The results
ing revealed that the amount of 2a affected the reac- demonstrated that all amino-directing groups have
tion: substrate 1a could be consumed completely, and some activity for the reaction; however, many were
the yield of 3 was increased slightly using 3 or less effective than the NHTs group except for the
4 equivalents of 2a (entries 12 and 13). It is notewor- NHBn group.
Table 3. Screening for the alkenes.[a]
[a]
Reaction conditions: 1a (0.3 mmol), 2 (3 equiv.), PdCl2 (5 mol%), Cu
ACHTUNGERTN(NUNG OAc)2
(1.5 equiv.) and DMA (3.0 mL) at 1408C under an O2 atmosphere for 48 h.
Adv. Synth. Catal. 2012, 354, 347 – 353
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Yan-Yun Liu et al.
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Table 4. Palladium-catalyzed synthesis of phenanthridines.[a]
[a]
Reaction conditions: 1 (0.3 mmol), 2a (3 equiv.), PdCl2 (5 mol%), Cu
ACHTUNGERTN(NUNG OAc)2
(1.5 equiv.) and DMA (3.0 mL) at 1408C under an O2 atmosphere for 48 h.
As shown in Table 3, numerous alkenes 2a–2k, sition of the aniline moiety (products 10–18). It was
were screened under the optimal reaction conditions. discovered that order of the Me-substituted substrate
It was found that terminal alkenes 2a–2j could under- activity was meta>para>othro in terms of yields.
go the reaction, providing the desired product 3 in While the meta-Me-substituted substrate regioselec-
22–67% yields. However, an internal alkene, bicyclo- tively gave product 11 in 75% yield, 4-methyl-N-(2’-
ACHTUNGTRENNUNG
under the optimal reaction conditions, and various 45%. Notably, the introduction of a chloro, a hetero-
biaryl-2-amine compounds underwent the reaction cycle or an olefinic group into this system makes this
with butyl acrylate (2a) in moderate to good yields methodology more valuable for the preparation of
(Table 4). Using 5 mol% of PdCl2, 1.5 equiv. pharmaceuticals and natural products (product 13, 16
CuACHTUNGTRENNUNG(OAc)2 and 1 atm O2, a number of substituents, and 17). Gratifyingly, a substrate with two Me groups
such as Me, F, Cl or CO2Me, on the aromatic ring of on the two different aryl rings of the biphenyl moiety
the N-phenyl moiety of the 2-yn-1-one were well tol- was also compatible with the optimal conditions
erated (products 4–9). The substrate bearing a p-Me (product 19).
group, for instance, reacted with PdCl2, Cu
G
To elucidate the mechanism, some control reactions
O2 smoothly to furnish the desired product 4 in 65% were carried out on the basis of the Miuraꢀs condi-
yield. Interestingly, monochloro- or dichloro-substitut- tions (Table 5).[6] It was found that only butyl 2-(5-
ed substrates were suitable substrates leading to the tosyl-5,6-dihydrophenanthridin-6-yl)acetate (20) was
corresponding chloro-containing products 6 and 9 in observed from the reaction of substrate 1a with
moderate yields, which provides a new route for the alkene 2a, CuACTHNUGTRENUNG(OAc)2, air, KOAc and MS 4 ꢂ in DMF
introduction of new functional groups into to this (Miuraꢀs conditions;[6] entry 1). Interestingly, the
system. We were pleased to find that a substrate with cleavage cyclization product 3 was isolated in 12%
an ester was also consistent with the optimized condi- yield when 150 mol% Cu
ACHTUNGRTEN(NUNG OAc)2 was added (entry 2).
tions (product 7). In light of the above results, several We speculate that Cu(OAc)2 may play the part of a
AHCTUNGTRENNUNG
substituents were tested, including Me, Cl, MeO, base to shift the selectivity. However, the reaction
OCH2O, vinyl and acetyl, on the aryl ring at the 2-po- provided a mixture of products in the presence of
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Palladium-Catalyzed Oxidative C C Bond Cleavage Cyclization of Biaryl-2-amines with Alkenes
Table 5. Control experiments on the basis of the Miuraꢀs conditions.[a]
Entry
[Pd] (mol%)
[Cu] (mol%)
Gas
Temperature [oC]
Isolated Yields [%]
20
3
1
2
3
4
Pd
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PdCl2
Pd(OAc)2
G
Cu
Cu
Cu
Cu
Cu
Cu
Cu
G
air
air
air
O2
O2
air
air
100
100
140
100
140
100
100
40
55
48
53
60
50
mixture
0
12
0
0
0
0
5
6
7[b]
trace
[a]
Reaction conditions: 1a (0.3 mmol), 2a (3 equiv.), [Pd] (5 mol%), Cu
(400 mg) and DMF (3 mL) for 48 h.
KOAc (1.5 equiv.).
ACHTUNGRTENUN(NG OAc)2, additive (1 atm), KOAc (0.5 equiv.), MS 4 ꢂ
[b]
À
1.5 equivalents of KOAc (entry 7). The results dem- and then C H functionalization forms intermediate
onstrated that both O2 and the reaction temperatures A, followed by 1,2-migratory insertion which affords
could not shift the chemoselectivity (entries 3–5). We intermediate B. Intermediate B undergoes b-H elimi-
found that PdCl2 was more effective than Pd
for the Miura cyclization reaction (entry 6).
ACHTUNGTRENNUNG
Some control experiments were conducted to un- ily complex with Pd(II) to yield intermediate D. Car-
derstand the mechanism, and the results are summar- boamination of intermediate D takes place to furnish
ized in Scheme 2. Notably, product 20 could not be intermediate E. Intermediate F is generated from the
converted into product 3 in the presence of PdCl2 reaction between intermediate E and O2 with the aid
(5 mol%), CuACHTUNGTRENNUNG(OAc)2 (1.5 equiv.) and DMA (3.0 mL) of CuACHTUNTGRENN(UGN OAc)2. Insertion of intermediate F gives inter-
at 1408C under an O2 atmosphere even for 72 h [Eq. mediate G, which is supported by the results of Eq.
(1)]. For the cyclization of N-Bn-substituted substrate (1) (Scheme 2): although intermediate H was ob-
1b with alkene 2a, another product (21), 5- served, the experimental results confirmed that prod-
benzylphen
the target product 3 in the presence of PdCl2, the results of Eq. (2) support the formation of inter-
Cu(OAc)2 and O2 at 1208C in DMA for 48 h [Eq. mediate E. The results of Eqs. (5) and (6) suggest that
ACHTUNGTRENNUNGanthridin-6(5H)-one, was obtained besides uct 3 was not derived from intermediate H. Notably,
ACHTUNGTRENNUNG
(2)]. However, product 21 could not be converted the leaving groups play a key role in the reaction
into product 3 under the optimal conditions (at from intermediate F to intermediate G. The reason
1408C). Interestingly, the solvent effect plays a key for the requirement of excess Cu
role in the chemoselectivity: only the Miura cycliza- the Pd(0) species need to be oxidized by Cu
tion product 22 was isolated in ClCH2CH2Cl, which regenerate the active Pd(II) in three steps. Moreover,
cannot be converted into product 3 under the optimal another role of Cu(OAc)2 may be to assist the forma-
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
À
conditions [Eq. (3)]. Using 1-nitro-4-vinylbenzene tion of intermediate C by cleaving the C Pd s-
(2k), 4-nitrobenzaldehyde (23) was observed in 53% bond.[12]
yield at 1208C [Eq. (4)]. It was interesting to disclose
that a C N bond cleavage of N-(4-nitrobenzyl)bi- catalyzed oxidative cleavage cyclization of biaryl-2-
phenyl-2-amine took place at 1208C leading to 4-ni- amines with alkenes involving C H oxidative olefina-
trobenzaldehyde (23) besides the desired product 3 tion and carboamination. This method displayed high
In summary, we have described a novel palladium-
À
À
[Eq. (5)]. However, the optimal conditions could be substrate compatibility: it tolerates a wide range of
À
used for the oxidative cleavage of alkene 24 or 1,2- biaryl-2-amines and alkenes for the C C bond oxida-
diol 26 to the corresponding aldehyde 25 in low yields tive cleavage cyclization through a tandem process.
[Eqs. (6) and (7)].[11] It is noteworthy that products 21 The mechanism was also discussed according to the
and 22 cannot be observed using N-(biphenyl-2-yl)-4- present results, particularly the control experiments.
methylbenzenesulfonamide (1a) as substrate.
Studies on applications of this oxidative cleavage cy-
ACHTUNGTRENcNGNU lization method in organic synthesis are underway.
Therefore, possible mechanisms as outlined in
Scheme 3 were proposed.[4–7] Complexation of Pd(II)
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Scheme 2. Control experiments
Scheme 3. Possible mechanisms.
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Palladium-Catalyzed Oxidative C C Bond Cleavage Cyclization of Biaryl-2-amines with Alkenes
[3] I. Moritani, Y. Fujiwara, Tetrahedron Lett. 1967, 1119.
Experimental Section
[4] For selected reviews, see: a) G. R. Newkome, W. E.
Puckett, V. K. Gupta, G. E. Kiefer, Chem. Rev. 1986,
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c) C. Jia, T. Kitamura, Y. Fujiwara, Acc. Chem. Res.
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Mares, J. Am. Chem. Soc. 1979, 101, 490; b) C. E. Houl-
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Typical Experimental Procedure for Palladium-
Catalyzed Synthesis of Phenanthridines
To a Schlenk tube were added N-(biphenyl-2-yl)-4-methyl-
benzenesulfonamide 1 (0.3 mmol), alkene 2 (0.90 mmol),
PdCl2 (5 mol%), CuACTHNUGTRNEUNG(OAc)2 (1.5 equiv.), and DMA (3 mL).
Then the tube was recharged with O2 (1 atm), and the mix-
ture was stirred at 1408C (oil bath temperature) for the indi-
cated time until complete consumption of starting material
as monitored by TLC and GC-MS analysis. After the reac-
tion was finished, the reaction mixture was diluted in diethyl
ether, and washed with brine. The aqueous phase was re-ex-
tracted with diethyl ether. The combined organic extracts
were dried over Na2SO4 and concentrated under vacuum,
and the resulting residue was purified by silica gel column
chromatography (hexane/ethyl acetate) to afford phenan-
thridines.
Phenanthridine (3):[8] White solid; mp 101.5–102.38C (un-
corrected); 1H NMR (500 MHz, CDCl3): d=9.20 (s, 1H),
8.50–8.13 (m, 2H), 8.20 (d, J=8.0 Hz, 1H), 7.95 (d, J=
7.5 Hz, 1H), 7.77 (t, J=7.5 Hz, 1H), 7.67 (t, J=7.0 Hz, 1H),
7.63–7.59 (m, 2H); 13C NMR (125 MHz, CDCl3): d=153.4,
144.2, 132.5, 131.1, 129.9, 128.8, 128.7, 127.5, 127.1, 126.2,
124.1, 122.2, 121.8; LR-MS (EI, 70 eV): m/z (%)=180
(M+ +1, 14), 179 (M+, 100), 151 (13), 76 (17).
[6] Amides or acids: M. Miura, T. Tsuda, T. Satoh, S.
Pivsa-Art, M. Nomura, J. Org. Chem. 1998, 63, 5211.
[7] Alcohols: a) A. Lu, D.-H. Wang, K. M. Engle, J.-Q. Yu,
J. Am. Chem. Soc. 2010, 132, 5916; phenols: b) M.
Miura, T. Tsuda, T. Satoh, M. Nomura, Chem. Lett.
1997, 1103; c) S. Aoki, J. Oyamada, T. Kitamura, Bull.
Chem. Soc. Jpn. 2005, 78, 468.
[8] a) A. R. Katritzky, C. W. Rees, E. F. Scriven, (Eds.),
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Heterocycl. Chem. 1981, 18, 223; c) T. Ishikawa, Med.
Res. Rev. 2001, 21, 61; d) W. A. Denny, Curr. Med.
Chem. 2002, 9, 1655; e) O. B. Abdel-Halim, T. Morika-
wa, S. Ando, H. Matsuda, M. Yoshikawa, J. Nat. Prod.
2004, 67, 1119; f) F. Viladomat, J. Bastida, G. Tribo, C.
Codina, M. Rubiralta, Phytochemistry 1990, 29, 1307.
[9] For the details see Table S1 in the Supporting Informa-
tion.
[10] a) W. C. P. Tsang, N. Zheng, S. L. Buchwald, J. Am.
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Acknowledgements
We thank the Natural Science Foundation of China (No.
20872112) and Fundamental Research Funds for the Central
Universities (Hunan University) for financial support.
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À
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