Cationic gold(l) axially chiral biaryl bisphosphine complex-catalyzed atropselective synthesis of heterobiaryls

Article abstract of DOI:10.3762/bjoc.7.105

It has been established that a cationic gold(I)/(R)-DTBM-Segphos or (R)-BINAP complex catalyzes the atropselective intramolecular hydroaiylation of alkynes leading to enantioenriched axially chiral 4-aryl-2-quinolinones and 4-arylcoumarins with up to 61% ee.

Full text of DOI:10.3762/bjoc.7.105

Cationic gold(I) axially chiral biaryl bisphosphine
complex-catalyzed atropselective synthesis
of heterobiaryls
Tetsuro Shibuya, Kyosuke Nakamura and Ken Tanaka*
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2011, 7, 944–950.
Department of Applied Chemistry, Graduate School of Engineering,
Tokyo University of Agriculture and Technology, Koganei, Tokyo
184-8588, Japan
doi:10.3762/bjoc.7.105
Received: 01 May 2011
Accepted: 22 June 2011
Published: 06 July 2011
Email:
Ken Tanaka* - tanaka-k@cc.tuat.ac.jp
This article is part of the Thematic Series "Gold catalysis for organic
synthesis".
* Corresponding author
Keywords:
Guest Editor: F. D. Toste
asymmetric catalysis; axial chirality; gold; heterobiaryls;
hydroarylation
© 2011 Shibuya et al; licensee Beilstein-Institut.
License and terms: see end of document.
Abstract
It has been established that a cationic gold(I)/(R)-DTBM-Segphos or (R)-BINAP complex catalyzes the atropselective intramolec-
ular hydroarylation of alkynes leading to enantioenriched axially chiral 4-aryl-2-quinolinones and 4-arylcoumarins with up to
61% ee.
Introduction
Atropselective biaryl synthesis [1-4] has attracted significant N-alkenyl-arylethynylamides leading to 4-aryl-2-pyridones
interest due to its great utility in asymmetric catalysis and (Scheme 1) [16,17].
natural product synthesis. In 2004, three research groups,
including ours, independently reported transition-metal
catalyzed asymmetric [2 + 2 + 2] cycloaddition reactions to
produce axially chiral biaryls [5-7]. These reports clearly
demonstrated the utility of the asymmetric annulation strategy
for the atropselective biaryl synthesis [8]. As an alternative
asymmetric annulation method for the atropselective biaryl syn-
thesis, we turned our attention to transition-metal catalyzed
hydroalkenylation and hydroarylation reactions [9-15]. In this
Scheme 1: Cationic gold(I)/PPh3-complex catalyzed intramolecular
hydroalkenylation of alkynes.
context, our research group developed the cationic gold(I)/
PPh3-complex catalyzed intramolecular hydroalkenylation of
944

Beilstein J. Org. Chem. 2011, 7, 944–950.
The atropselective synthesis of 6-aryl-2-pyridones has already
been achieved by rhodium catalyzed [2 + 2 + 2] cycloaddition
[18], while the atropselective synthesis of 4-aryl-2-pyridones
has not yet been realized. The application of this intramolecular
hydroalkenylation reaction to the atropselective synthesis of
4-aryl-2-pyridones from N-alkenyl-arylethynylamides was thus
investigated. Although cationic gold(I)/axially chiral biaryl
bisphosphine complexes [19-31] have been frequently
employed in asymmetric variants of cationic gold(I) catalyses
[32-38], including 6-endo-dig and 6-exo-dig cyclizations [39-
41], the use of these gold(I) complexes gave almost racemic
products [42]. Fortunately, cationic palladium(II)/axially chiral
Scheme 3: Cationic palladium(II)/(S)-xyl-H8-BINAP complex-catalyzed
atropselective intramolecular hydroarylation of alkynes.
biaryl bisphosphine complexes were found to be effective cata- leading to axially chiral 4-aryl-2-quinolinones, and the cationic
lysts, and a cationic palladium(II)/(S)-xyl-Segphos complex palladium(II)/(S)-xyl-H8-BINAP complex showed the highest
showed the highest enantioselectivity (Scheme 2) [42].
enantioselectivity (Scheme 3) [43,44].
In this paper, we report the use of the cationic gold(I)/axially
chiral biaryl bisphosphine complexes in the catalytic asym-
metric intramolecular hydroarylation for the synthesis of axially
chiral 4-aryl-2-quinolinones and 4-arylcoumarins.
Results and Discussion
The reaction of N-benzyl-N-(2-naphthyl)propiolamide 1a,
bearing a 2-methoxynaphthyl group at an alkyne terminus, was
first investigated in the presence of a cationic gold(I)/(R)-
BINAP complex (20 mol % Au). Although the reaction
proceeded at room temperature in good yield, enantio-
Scheme 2: Cationic palladium(II)/(S)-xyl-Segphos-complex catalyzed
atropselective intramolecular hydroalkenylation of alkynes.
In addition, the cationic palladium(II)/axially chiral biaryl selectivity was low (Table 1, entry 1). The effect of axially
bisphosphine complexes were able to catalyze the asymmetric chiral biaryl bisphosphine ligands (Figure 1) on the yield and
intramolecular hydroarylation of N-aryl-arylethynylamides the enantioselectivity was then investigated. Among the
Table 1: Screening of axially chiral biaryl bisphosphine ligands for the cationic gold(I)-complex catalyzed atropselective intramolecular hydroarylation
of 1a.a
Entry
Ligand
Convn (%)b
Yield (%)c
ee (%)
1
(R)-BINAP
81
75
81
93
96
96
49
7 (S)
2
(R)-Segphos
90
8 (R)
3
(R)-H8-BINAP
94
17 (S)
13 (R)
59 (R)
31 (R)
4
(S)-xyl-H8-BINAP
(R)-DTBM-Segphos
(R)-DTBM-Segphos
100
100
71
5
6d
aAuCl(SMe2) (0.010 mmol, 20 mol %), AgBF4 (0.010 mmol, 20 mol %), ligand (0.0050 mmol, 10 mol %), 1a (0.050 mmol), and (CH2Cl)2 (1.5 mL)
were used. bDetermined by 1H NMR. cIsolated yield. dAuCl(SMe2) (0.010 mmol, 10 mol %), AgBF4 (0.010 mmol, 10 mol %), ligand (0.0050 mmol, 5
mol %), 1a (0.10 mmol), and (CH2Cl)2 (1.5 mL) were used. Reaction time: 72 h.
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Beilstein J. Org. Chem. 2011, 7, 944–950.
Figure 1: Structures of axially chiral biaryl bisphosphine ligands.
bis(diphenylphosphine) ligands examined (Table 1, entries 2-methoxynaphthalene derivative 1a (Table 2, entry 1) and the
1–3), the use of (R)-H8-BINAP furnished 2a with the highest 2-methoxymethoxynaphthalene derivative 1b (Table 2, entry 2)
enantiomeric excess (Table 1, entry 3). An increase in the steric furnished the desired benzoquinolinones 2a and 2b, respective-
bulk of the aryl group on the phosphorus atom of H8-BINAP ly, in high yields and high ee, using (R)-DTBM-Segphos as a
lead to a decrease in the ee (Table 1, entry 4). The use of steri- ligand. In addition, benzocoumarin 2c (Table 2, entry 3) was
cally more demanding (R)-DTBM-Segphos as a ligand obtained in moderate ee, although the yield was low due to
furnished 2a in high yield with the highest ee (Table 1, entry 5). partial deprotection of the methoxymethoxynaphthalene moiety
Unfortunately, a reduction in the amount of gold to 10 mol % (Table 2, entry 3). The reactions of carbazole and dialkoxyben-
significantly decreased both product yield and enantio- zene derivatives 1d–g, using (R)-DTBM-Segphos as a ligand,
selectivity (Table 1, entry 6).
furnished the corresponding quinolinone and coumarin deriva-
tives 2d–g in high yields with perfect regioselectivity, while the
Thus, the scope of the cationic gold(I)-complex catalyzed observed ee values were very low (<10% ee). However, inter-
atropselective intramolecular hydroarylation of alkynes was estingly, the use of (R)-BINAP as a ligand improved the enan-
explored at room temperature, as shown in Table 2. The toselectivity (14–32% ee, Table 2, entries 4–7).
Table 2: Cationic gold(I)-complex catalyzed atropselective intramolecular hydroarylation of 1a–g leading to heterobiaryls 2a–g.a
Entry
Ligand
(time)
% yieldb (% ee)
1
2
(R)-DTBM-
Segphos
(40 h)
1
1a
1b
1c
(R)-(−)-2a
96 (59)
(R)-DTBM-
Segphos
(72 h)
2
(−)-2b
87 (61)
(R)-DTBM-
Segphos
(40 h)
3
(−)-2c
33 (49)
946

Beilstein J. Org. Chem. 2011, 7, 944–950.
Table 2: Cationic gold(I)-complex catalyzed atropselective intramolecular hydroarylation of 1a–g leading to heterobiaryls 2a–g.a (continued)
(R)-BINAP
(72 h)
4
1d
(+)-2d
82 (28)
(R)-BINAP
(40 h)
5
6
7
1e
(−)-2e
(+)-2f
(+)-2g
100 (32)
88 (27)
93 (14)
(R)-BINAP
(40 h)
1f
(R)-BINAP
(40 h)
1g
aReactions were conducted using AuCl(SMe2) (0.010 mmol), AgBF4 (0.010 mmol), (R)-DTBM-Segphos or (R)-BINAP (0.0050 mmol), 1a–g (0.050
mmol), and (CH2Cl)2 (1.5 mL) at rt. In all entries, 100% convn of substrates 1a–g was observed.
bIsolated yield.
In the previously reported cationic palladium(II)/(S)-xyl-H8- complex furnished the corresponding benzoquinolinone 2h with
BINAP-complex catalyzed atropselective intramolecular lower yield and ee than those of 2a (Scheme 4).
hydroarylation of alkynes, the presence of the 2-methoxy-
substituted aryl group at the alkyne terminus was important for Conclusion
the realization of both high reactivity and enantioselectivity In conclusion, it has been established that a cationic gold(I)/(R)-
[40]. Similarly, the reaction of 2-methylnaphthalene derivative DTBM-Segphos or (R)-BINAP complex catalyzes the atropse-
1h in the presence of the cationic gold(I)/(R)-DTBM-Segphos lective intramolecular hydroarylation of alkynes leading to
Scheme 4: Cationic gold(I)/(R)-DTBM-Segphos-complex catalyzed atropselective intramolecular hydroarylation of 2-methylnaphthalene derivative 1h.
947

Beilstein J. Org. Chem. 2011, 7, 944–950.
enantioenriched axially chiral 4-aryl-2-quinolinones and 4-aryl- 8.4 Hz, 1H), 7.96 (d, J = 9.2 Hz, 1H), 7.80 (d, J = 8.1 Hz, 1H),
coumarins in up to 61% ee. Although there clearly remains 7.59 (dd, J = 8.1, 6.5 Hz, 1H), 7.42 (dd, J = 8.4, 6.5 Hz, 1H),
room for improvement in enantioselectivity, the present asym- 7.26 (d, J = 9.2 Hz, 1H), 6.43 (d, J = 2.1 Hz, 2H), 6.40 (t, J =
metric catalysis is a rare example of the utilization of gold(I)/ 2.1 Hz, 1H), 4.06 (s, 3H), 3.80 (s, 6H); 13C NMR (CDCl3, 125
chiral phosphine catalysts for the construction of noncentrochi- MHz) δ 162.1, 161.1, 152.5, 151.8, 135.0, 133.6, 128.4, 128.3,
rality [45-47].
128.1, 124.7, 112.1, 101.8, 100.2, 98.7, 89.3, 85.0, 56.5, 55.5;
HRMS–ESI (m/z): [M + Na]+ calcd for C22H18O5Na, 385.1046;
found, 385.1047.
Experimental
General: 1H NMR spectra were recorded at 300 MHz (JEOL
AL 300). 13C NMR spectra were obtained with complete proton General procedure for cationic gold(I)/axially chiral biaryl
decoupling at 75 MHz (JEOL AL 300). HRMS data were bisphosphine complex-catalyzed atropselective intramolec-
obtained on a Bruker micrOTOF Focus II. Infrared spectra were ular hydroarylation of N-aryl-arylethynylamides 1: To
obtained on a JASCO FT/IR-4100. Optical rotations were AuCl(SMe2) (0.010 mmol) was added a solution of axially
obtained on a JASCO DIP-1000. Melting points were obtained chiral biaryl bisphosphine ligand (0.0050 mmol) in (CH2Cl)2
on a METTLER MP50. Anhydrous (CH2Cl)2 (No. 28,450-5) (0.5 mL), and the mixture was stirred at room temperature for 1
was purchased from Aldrich and used as received. Solvents for h. To this solution was added AgBF4 (0.010 mmol) in (CH2Cl)2
the synthesis of substrates were dried over molecular sieves (0.5 mL) at room temperature, and the mixture was stirred at
(4 Å, Wako) prior to use. Substrates 1a, 1b, 1d, 1e, 1f, and 1h room temperature for 0.5 h. To this mixture was added a solu-
were prepared according to the literature [43]. Products 2a, 2b, tion of 1 (0.050 mmol) in (CH2Cl)2 (0.5 mL) at room tempera-
2d, 2e, 2f, and 2h were already reported [43]. All other reagents ture. After stirring at room temperature for 40–72 h, the mix-
were obtained from commercial sources and used as received. ture was directly purified on a preparative TLC to afford 2.
All reactions were carried out under an atmosphere of argon or
nitrogen in oven-dried glassware with magnetic stirring.
(−)-1-(2-Methoxymethoxynaphthalen-1-yl)benzo[f]chromen-
3-one [(−)-2c]: Colorless solid; mp 169.4–170.8 °C; [α]25D
(2-Methoxymethoxynaphthalen-1-yl)propynoic acid naph- −86.1 (c 0.28, CHCl3, 49% ee); IR (KBr): 1738, 1510, 1244,
thalen-2-yl ester (1c): To a stirred solution of 3-[2- 1050, 1011 cm−1; 1H NMR (CDCl3, 500 MHz) δ 8.05 (d, J =
(methoxymethoxy)-1-naphthalenyl]-2-propynoic acid [48] 8.7 Hz, 1H), 8.02 (d, J = 9.2 Hz, 1H), 7.92 (d, J = 8.4 Hz, 1H),
(0.256 g, 1.00 mmol), 2-naphthol (0.159 g, 1.10 mmol), and 7.81 (d, J = 8.0 Hz, 1H), 7.62 (d, J = 8.7 Hz, 1H), 7.57 (d, J =
4-dimethylaminopyridine (12.2 mg, 0.100 mmol) in CH2Cl2 (10 9.2 Hz, 1H), 7.53 (d, J = 8.4 Hz, 1H), 7.42 (ddd, J = 8.4, 7.0,
mL) was added a solution of dicyclohexylcarbodiimide (0.248 1.4 Hz, 1H), 7.36 (ddd, J = 8.4, 6.9, 1.5 Hz, 1H), 7.32 (ddd, J =
g, 1.20 mmol) in CH2Cl2 (3 mL) at 0 °C, and the mixture was 8.0, 7.0, 1.0 Hz, 1H), 7.17 (d, J = 8.3 Hz, 1H), 6.97 (ddd, J =
stirred at 0 °C for 2 h and at room temperature for 18 h. The 8.3, 6.9, 1.4 Hz, 1H), 6.45 (s, 1H), 5.04 (dd, J = 22.4, 6.9 Hz,
crude mixture was filtered with CH2Cl2. The filtrate was 2H), 3.05 (s, 3H); 13C NMR (CDCl3, 125 MHz) δ 160.6, 154.8,
washed with brine, dried over Na2SO4, and concentrated. The 152.5, 150.6, 133.8, 131.6, 131.0, 130.9, 129.8, 129.5, 129.0,
residue was purified by a silica gel column chromatography 128.2, 127.7, 127.6, 125.4, 124.8, 124.4, 123.8, 122.8, 118.6,
(hexane/EtOAc = 10:1) to give 1c (0.222 g, 0.580 mmol, 58% 117.8, 115.7, 114.2, 94.2, 56.0; HRMS–ESI (m/z): [M + Na]+
yield). Yellow solid; mp 97.3–99.3 °C; IR (KBr): 2203, 1717, calcd for C25H18O4Na, 405.1097; found, 405.1085;
1229, 1149, 1005 cm−1; 1H NMR (CDCl3, 300 MHz) δ CHIRALPAK OD-H, hexane/iPrOH = 80:20, 1.0 mL/min,
8.15–8.01 (m, 1H), 7.97–7.70 (m, 6H), 7.61–7.31 (m, 6H), 5.36 retention times: 14.3 min (major isomer) and 19.0 min (minor
(s, 2H), 3.56 (s, 3H); 13C NMR (CDCl3, 125 MHz) δ 160.0, isomer).
152.8, 148.1, 134.7, 133.7, 133.4, 131.7, 129.7, 128.8, 128.3,
127.82, 127.79, 126.7, 126.0, 125.1, 124.8, 121.0, 118.8, 115.5, (+)-5,7-Dimethoxy-4-(2-methoxynaphthalen-1-yl)chromen-
103.8, 95.1, 89.1, 85.2, 56.6; HRMS–ESI (m/z): [M + Na]+ 2-one [(+)-2g]: Colorless solid; mp 148.8–150.4 °C; [α]25D
calcd for C25H18O4Na, 405.1097; found, 405.1107.
+44.9 (c 0.24, CHCl3, 14% ee); IR (KBr): 1718, 1618, 1598,
1351, 1114 cm−1; 1H NMR (CDCl3, 300 MHz) δ 7.88 (d, J =
(2-Methoxynaphthalen-1-yl)propynoic acid 3,5-dimethoxy- 9.0 Hz, 1H), 7.85–7.77 (m, 1H), 7.48–7.39 (m, 1H), 7.38–7.27
phenyl ester (1g): The title compound was prepared from (m, 3H), 6.57 (d, J = 2.4 Hz, 1H), 6.12 (d, J = 2.4 Hz, 1H), 6.07
(2-methoxynaphthalen-1-yl)propynoic acid [49] and 3,5- (s, 1H), 3.85 (s, 3H), 3.83 (s, 3H) 3.07 (s, 3H); 13C NMR
dimethoxyphenol in 70% yield by the procedure used for 1c. (CDCl3, 125 MHz) δ 163.1, 161.2, 158.5, 157.1, 152.4, 151.0,
Yellow solid; mp 102.9–104.7 °C; IR (KBr): 2211, 1714, 1621, 131.9, 129.3, 128.5, 127.9, 126.6, 124.2, 123.6, 122.9, 114.0,
1269, 1156 cm−1; 1H NMR (CDCl3, 300 MHz) δ 8.16 (d, J = 113.1, 105.0, 95.8, 93.6, 56.7, 55.75, 55.71; HRMS–ESI (m/z):
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Beilstein J. Org. Chem. 2011, 7, 944–950.
17.Imase, H.; Tanaka, K. Chem. Lett. 2009, 38, 1152–1153.
[M + Na]+ calcd for C22H18O5Na, 385.1046; found, 385.1036;
CHIRALPAK AD-H, hexane/iPrOH = 80:20, 1.0 mL/min,
retention times: 8.8 min (minor isomer) and 10.5 min (major
isomer).
doi:10.1246/cl.2009.1152
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doi:10.1021/ol052041b
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Angew. Chem., Int. Ed. 2010, 49, 598–601.
Supporting Information
doi:10.1002/anie.200905000
Supporting Information File 1
1H and 13C NMR spectra for new compounds 1c, 1g, 2c,
and 2g.
21.Kleinbeck, F.; Toste, F. D. J. Am. Chem. Soc. 2009, 131, 9178–9179.
doi:10.1021/ja904055z
22.Zhang, Z.; Lee, S. D.; Widenhoefer, R. A. J. Am. Chem. Soc. 2009,
131, 5372–5373. doi:10.1021/ja9001162
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-7-105-S1.pdf]
23.Uemura, M.; Watson, I. D. G.; Katsukawa, M.; Toste, F. D.
J. Am. Chem. Soc. 2009, 131, 3464–3465. doi:10.1021/ja900155x
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Acknowledgements
25.Chao, C.-M.; Vitale, M. R.; Toullec, P. Y.; Genêt, J.-P.; Michelet, V.
Chem.–Eur. J. 2009, 15, 1319–1323. doi:10.1002/chem.200802341
26.Luzung, M. R.; Mauleón, P.; Toste, F. D. J. Am. Chem. Soc. 2007, 129,
12402–12403. doi:10.1021/ja075412n
This work was supported partly by a Grant-in-Aid for Scien-
tific Research (No. 20675002) from MEXT, Japan. We thank
Takasago International Corporation for the donation of
Segphos, H8-BINAP, xyl-H8-BINAP, and DTBM-Segphos.
27.Tarselli, M. A.; Chianese, A. R.; Lee, S. J.; Gagné, M. R.
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