Palladium-catalyzed decarboxylative coupling of benzoic acid derivatives using hydrazone ligands

DOI: 10.1016/j.tetlet.2014.04.017

Source and publish data:

Tetrahedron Letters p. 3184 - 3188 (2014)

Update date:2022-08-04

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Authors:

Mino, Takashi

Yoshizawa, Eri

Watanabe, Kohei

Abe, Taichi

Hirai, Kiminori

Sakamoto, Masami

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Article abstract of DOI:10.1016/j.tetlet.2014.04.017

Palladium-catalyzed decarboxylative coupling of benzoic acid derivatives with arylboroxins gave biaryls using a catalytic amount of Pd(TFA) ₂-hydrazone 1d system with Ag₂CO₃ at 80 °C in good yields. We also found that decarboxylative coupling with aryl(trialkoxy)silanes gave biaryls using a Pd(TFA)₂-hydrazone 1g system with AgF in good yields.

Full text of DOI:10.1016/j.tetlet.2014.04.017

Tetrahedron Letters 55 (2014) 3184–3188

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Palladium-catalyzed decarboxylative coupling of benzoic acid

derivatives using hydrazone ligands

⇑

Takashi Mino , Eri Yoshizawa, Kohei Watanabe, Taichi Abe, Kiminori Hirai, Masami Sakamoto

Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

a r t i c l e i n f o

a b s t r a c t

Article history:

Palladium-catalyzed decarboxylative coupling of benzoic acid derivatives with arylboroxins gave biaryls

using a catalytic amount of Pd(TFA)₂–hydrazone 1d system with Ag₂CO₃at 80 °C in good yields. We also

found that decarboxylative coupling with aryl(trialkoxy)silanes gave biaryls using a Pd(TFA)₂–hydrazone

1g system with AgF in good yields.

Received 10 March 2014

Revised 2 April 2014

Accepted 7 April 2014

Available online 13 April 2014

Keywords:

Palladium catalyst

Decarboxylative coupling

Arylboroxin

Aryl(trialkoxy)silane

Palladium-catalyzed coupling reactions of aryl halides with aryl

organometallics, such as the Suzuki–Miyaura coupling and Hiyama

coupling, have become common and convenient synthetic meth-

ods in organic chemistry for biaryl compounds.¹On the other hand,

the Myers group reported a palladium-catalyzed decarboxylative

Heck reaction of benzoic acid derivatives, instead of aryl halides,

with oleﬁns in 2002.²After the Gooßen group³and the Forgione

group⁴independently reported the palladium-catalyzed decarb-

oxylative coupling of benzoic acid derivatives, instead of arylbo-

ronic acids, with aryl bromides in 2006, the Becht group⁵and the

Liu group⁶also reported the palladium-catalyzed decarboxylative

coupling with aryl halides. More recently, the Liu group⁷and the

Tan group⁸reported the palladium-catalyzed decarboxylative cou-

pling of benzoic acid derivatives with arylboronic acids or six-

membered boronic acid esters under high reaction temperature

(120–130 °C). However, palladium-catalyzed decarboxylative cou-

pling of benzoic acids with other arylboronic acid derivatives, such

as arylboroxins, and aryl(trialkoxy)silanes has not been reported.

We recently demonstrated air-stable hydrazone as an effective

ligand in such palladium-catalyzed CAC bond formations as the

Suzuki–Miyaura coupling⁹the Mizoroki–Heck type reaction,¹⁰

the Sonogashira coupling,¹¹the Hiyama coupling,^11aand the allyl

cross-coupling reactions.¹²We now report the use of hydrazone

ligands 1–3 (Fig. 1) for a palladium-catalyzed decarboxylative cou-

pling of benzoic acids with arylboroxins and aryl(trialkoxy)silanes.

Figure 1. Hydrazone ligands.

Initially, we sought the optimal reaction conditions for a palla-

dium-catalyzed decarboxylative coupling of the benzoic acid deriv-

ative with arylboroxin using the hydrazone ligand. 2,4,6-

Trimethoxybenzoic acid and tri-p-tolylboroxin (3a) were chosen

as model substrates with 7.5 mol % of Pd catalyst for 2 h under

an air atmosphere at 80 °C (Table 1). Using 7.5 mol % of hydrazone

1a as a ligand, we observed that the decarboxylative coupling in

the presence of Pd(TFA)₂with Ag₂CO₃in DMSO as a solvent pro-

ceeded to give the corresponding product 4a in 38% yield (Table 1,

entry 1). We tested other hydrazones 1b–e, 1h, 2, and 3 and found

that hydrazone 1d was an effective ligand for this reaction (entry

4). Without ligand, the reaction gave low yields of the desired

⇑

Corresponding author. Tel.: +81 43 290 3385; fax: +81 43 290 3401.

E-mail address: tmino@faculty.chiba-u.jp (T. Mino).

http://dx.doi.org/10.1016/j.tetlet.2014.04.017

T. Mino et al. / Tetrahedron Letters 55 (2014) 3184–3188

3185

Table 1

Optimization of reaction conditions for the palladium-catalyzed decarboxylative coupling of 2,4,6-trimethoxybenzoic acid with tri-p-tolylboroxin^a

Entry

Ligand

Pd catalyst

Additive

Solvent

Yield^b(%)

11^c

12^d

13^e

14^f

Pd(TFA)₂

Pd(OAc)₂

Pd(acac)₂

PdCl₂

PdCl₂(MeCN)₂

Pd₂(dba)₃ÁCHCl₃

Pd(TFA)₂

Ag₂CO₃

Ag₂O

DMSO

DMSO/H₂O (3:1)

DMAc

DMF

Trace

—

PPh₃(15 mol %)

AgOAc (6.0 equiv)

AgF (6.0 equiv)

Ag₂CO₃

NMP

PhMe

Trace

Reaction conditions: 2,4,6-trimethoxybenzoic acid, tri-p-tolylboroxin (0.67 equiv), ligand (7.5 mol %), Pd source (Pd = 7.5 mol %), additive (3.0 equiv), solvent (0.2 M) at

80 °C for 2 h under air.

Isolated yields.

0.40 mmol of p-tolylboronic acid was used instead of tri-p-tolylboroxin.

0.40 mmol of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)toluene was used instead of tri-p-tolylboroxin.

0.40 mmol of p-tolylboronic acid MIDA ester was used instead of tri-p-tolylboroxin.

0.40 mmol of potassium p-tolyltriﬂuoroborate was used instead of tri-p-tolylboroxin.

product (entry 9). Using PPh₃as the ligand, the reaction also gave

low yields of the desired product (entry 10). When we used other

organoboron compounds including p-tolylboronic acid, the yields

decreased (entries 11–14). We also investigated the effect of vari-

ous palladium sources (entry 4 vs entries 15–19), additives (entry 4

vs entries 20–22), and solvents (entry 4 vs entries 23–27). Using

Pd(TFA)₂with Ag₂CO₃in DMSO led to good yields for this reaction

(entry 4).

Under optimized reaction conditions, the effect of various aryl-

boroxins in the decarboxylative coupling was investigated using

2,4,6-trimethoxybenzoic acid (Table 2).¹³Using tri-p-tolylboroxin

(3a), tri-m-tolylboroxin (3b) and triphenylboroxin (3d) led to good

yields of the corresponding products (entries 1, 2 and 4). Para- and

meta-substituted arylboroxins also gave products with moderate

to good yields (entries 5–8). Unfortunately, the reaction with tri-

o-tolylboroxin (3c) and tri-1-naphthylboroxin (3i) did not give

the corresponding products 4c and 4i (entries 3 and 9). Tri-2-naph-

thylboroxin (3j) and tri-3,4-dichlorophenylboroxin (3k) led to

good yields of the corresponding products (entries 10 and 11).

The reaction of 2,4,6-triethoxybenzoic acid with tri-p-anisylborox-

in (3h) gave the corresponding product 4l in 15% yield (entry 12).

We also tested the reaction of 2,3,4,6-tetramethoxybenzoic acid

and 2,6-dimethoxybenzoic acid. The reaction with tri-3,4-dichlor-

ophenylboroxin (3k) gave the corresponding products 4m and 4n

in low yields (entries 13 and 14).

We next tried the use of the hydrazone ligand for a palladium-

catalyzed decarboxylative coupling with aryl(trialkoxy)silanes

instead of arylboroxins. We sought the optimal reaction conditions

for decarboxylative coupling of 2,4,6-trimethoxybenzoic acid with

p-tolyl(triethoxy)silane (5a) as model substrates with 7.5 mol % of

Pd catalyst for 2 h under an air atmosphere at 100 °C (Table 3).

Using 7.5 mol % of hydrazone 1d as a ligand, we observed that

the decarboxylative coupling in the presence of Pd(TFA)₂with

AgF in DMAc as a solvent proceeded to give the corresponding

product 4a in 53% yield (Table 3, entry 1). We tested other hydra-

zones 1e–h, 2, and 3 and found that hydrazone 1g was an effective

ligand for this reaction (entry 4). Without ligand, the reaction gave

low yields of the desired product (entry 8). Using PPh₃as a ligand,

the reaction also gave low yields of the desired product (entry 9).

We investigated the effect of various palladium sources and addi-

tives (entries 10–15). Using Pd(TFA)₂with AgF led to good yields

for this reaction (entry 4). Several solvents were also tested

3186

T. Mino et al. / Tetrahedron Letters 55 (2014) 3184–3188

Table 2

Palladium-catalyzed decarboxylative coupling of benzoic acid derivatives with arylboroxins^a

Entry

Product

Yield^b(%)

p-MeC₆H₄(3a)

m-MeC₆H₄(3b)

o-MeC₆H₄(3c)

Ph (3d)

p-ClC₆H₄(3e)

m-ClC₆H₄(3f)

p-FC₆H₄(3g)

p-MeOC₆H₄(3h)

1-Naph (3i)

12^c

13^d

14^e

2-Naph (3j)

3,4-DiClC₆H₃(3k)

p-MeOC₆H₄(3h)

3,4-DiClC₆H₃(3k)

Reaction conditions: 2,4,6-trimethoxybenzoic acid, arylboroxin (0.67 equiv), ligand 1d (7.5 mol %), Pd(TFA)₂(7.5 mol %), Ag₂CO₃(3.0 equiv), DMSO (0.2 M) at 80 °C for 2 h

under air.

Isolated yields.

2,4,6-Triethoxybenzoic acid was used instead of 2,4,6-trimethoxybenzoic acid.

2,3,4,6-Tetramethoxybenzoic acid was used instead of 2,4,6-trimethoxybenzoic acid.

2,6-Dimethoxybenzoic acid was used instead of 2,4,6-trimethoxybenzoic acid.

Table 3

Optimization of reaction conditions on the palladium-catalyzed decarboxylative coupling of 2,4,6-trimethoxybenzoic acid with p-tolyl(triethoxy)silane^a

Entry

Ligand

Pd catalyst

Additive

Solvent

Yield^b(%)

21^c

Pd(TFA)₂

Pd(OAc)₂

PdCl₂

Pd(acac)₂

Pd(TFA)₂

AgF

Ag₂O

Ag₂CO₃

AgOAc

AgF

DMAc

DMSO

DMF

–

PPh₃(15 mol %)

NMP

AgF

PhMe

MeCN

DMAc

Reaction conditions: p-tolyl(triethoxy)silane, 2,4,6-trimethoxybenzoic acid (2.0 equiv), ligand (7.5 mol %), Pd source (7.5 mol %), additive (Ag = 3.0 equiv), solvent (0.2 M)

at 100 °C for 2 h under air.

Isolated yields.

This reaction was carried out at 110 °C.

(entries 16–20). DMAc was the most effective base in this reaction

(entry 4). Finally, the reaction was carried out at 110 °C, and the

yield increased to 66% (entry 21).

Under optimized reaction conditions, the effect of various

aryl(trialkoxy)silanes in the decarboxylative coupling was

investigated using 2,4,6-trimethoxybenzoic acid (Table 4).¹⁴Using

T. Mino et al. / Tetrahedron Letters 55 (2014) 3184–3188

3187

Table 4

Palladium-catalyzed decarboxylative coupling of benzoic acid derivatives with aryl(trialkoxy)silanes^a

Entry

Product

Yield^b(%)

1^c

p-MeC₆H₄(5a)

Ph (5b)

3^c,d

p-ClC₆H₄(5c)

p-MeOC₆H₄(5d)

p-CF₃C₆H₄(5e)

p-MeOC₆H₄(5d)

2-Thiophenyl (3f)

p-MeC₆H₄(5g)

Ph (5h)

5^e

6^f

9^e

10^c

p-MeOC₆H₄(5i)

Reaction conditions: aryl(trialkoxy)silane, 2,4,6-trimethoxybenzoic acid (2.0 equiv), ligand 1g (7.5 mol %), Pd(TFA)₂(7.5 mol %), AgF (3.0 equiv), DMAc (0.2 M) at 100 °C

for 2 h under air.

Isolated yields.

This reaction was carried out at 110 °C.

This reaction was carried out for 8 h.

This reaction was carried out for 4 h.

2,4,6-Triethoxybenzoic acid was used instead of 2,4,6-trimethoxybenzoic acid.

p-tolyl(triethoxy)silane, phenyl(triethoxy)silane, and p-anisyl(tri-

ethoxy)silane led to good yields of the corresponding products

for 2 h (entries 1, 2, and 4). When the reaction with p-chloro-

phenyl(triethoxy)silane was carried out for 8 h, the reaction also

gave the corresponding product 4e in good yields (entry 3). Using

4-triﬂuoromethylphenyl(triethoxy)silane (5e) led to moderate

yield of the corresponding product 4o (entry 5). Moreover, the

reaction of 2,4,6-triethoxybenzoic acid with p-anisyl(trieth-

oxy)silane (5d) gave the product in 41% yield (entry 6).

Unfortunately, the reaction with heteroaryl triethoxysilane such

as 2-thiophenyltriethoxysilane (3f) gave the corresponding

product 4p in low yields (entry 7). On the other hand, the reaction

of 2,4,6-trimethoxybenzoic acid with aryl(trimethoxy)silanes 5g–i

gave products 4a, 4d, and 4h in good yields (entries 8–10).

A plausible mechanism for decarboxylative coupling of benzoic

acid derivatives is illustrated in Scheme 1. The ﬁrst step is the

decarboxylation of benzoic acid derivatives. We thought that this

step proceeded smoothly by using the Pd(II)–hydrazone complex

at 80 °C. Subsequently, the transmetallation of Pd complex with

arylboroxin or aryl(trialkoxy)silane followed by reductive elimina-

tion gives the coupling product and Pd(0)–hydrazone complex.

Finally reoxidation of Pd(0) by the Ag(I) salts gives the Pd(II)–

hydrazone complex, and the catalytic cycle is completed.

In summary, we found that palladium-catalyzed decarboxyla-

tive coupling of 2,4,6-trimethoxybenzoic acid with arylboroxins

or aryl(trialkoxy)silanes gave the corresponding biaryls using a

catalytic amount of Pd(TFA)₂–hydrazone system in good yields.

Supplementary data

Supplementary data associated with this article can be found,

in the online version, at http://dx.doi.org/10.1016/j.tetlet.2014.04.

017.

References and notes

1. For some reviews, see: (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995 , 95 , 2457–

2483; (b) Stanforth, S. P. Tetrahedron 1998 , 54 , 263–303; (c) Suzuki, A. In Metal-

Catalyzed Cross-Coupling Reactions ; Diederich, F., Stang, P. J., Eds.; Wiley-VCH:

Weinheim, 1998; pp 49–97; (d) Negishi, E.-I. In Handbook of Organopalladium

Chemistry For Organic Synthesis ; Negishi, E.-I., Ed.; John Wiley & Sons: New

York, 2002; pp 229–994; (e) Dumrath, A.; Lübbe, C.; Beller, M. In Palladium-

Catalyzed Coupling Reactions ; Molnár, Á., Ed.; Wiley-VCH: Weinheim, 2013; pp

445–490.

2. (a) Myers, A. G.; Tanaka, D.; Mannion, M. R. J. Am. Chem. Soc. 2002 , 124 , 11250–

11251; For some reviews, see: (b) Rodríguez, N.; Gossen, L. J. Chem. Soc. Rev.

2011 , 40 , 5030–5048; (c) Shang, R.; Liu, L. Sci. China Chem. 2011 , 54 , 1670–

1687; (d) Cornella, J.; Larrosa, I. Synthesis 2012 , 44 , 653–676.

3. Gooßen, L. J.; Deng, G.; Levy, L. M. Science 2006 , 313 , 662–664.

4. Forgione, P.; Brochu, M.-C.; St-Onge, M.; Thesen, K. H.; Bailey, M. D.; Bilodeau,

F. J. Am. Chem. Soc. 2006 , 128 , 11350–11351.

5. (a) Becht, J.-M.; Catala, C.; Le Drian, C.; Wagner, A. Org. Lett. 2007 , 9 , 1781–

1783; (b) Becht, J.-M.; Le Drian, C. Org. Lett. 2008 , 10 , 3161–3164.

Scheme 1. A plausible mechanism for decarboxylative coupling of benzoic acid

derivatives.

3188

T. Mino et al. / Tetrahedron Letters 55 (2014) 3184–3188

6. Shang, R.; Xu, Q.; Jiang, Y.-Y.; Wang, Y.; Lie, L. Org. Lett. 2010 , 12 , 1000–1003.

7. Dai, J.-J.; Liu, J.-H.; Luo, D.-F.; Liu, L. Chem. Commun. 2011 , 47 , 677–679.

8. Wang, A.; Li, X.; Liu, J.; Gui, Q.; Chen, X.; Tan, Z.; Xie, K. Synth. Commun. 2014 ,

44 , 289–295.

9. (a) Mino, T.; Shirae, Y.; Sakamoto, M.; Fujita, T. Synlett 2003 , 882–884; (b) Mino,

T.; Shirae, Y.; Sakamoto, M.; Fujita, T. J. Org. Chem. 2005 , 70 , 2191–2194.

10. (a) Mino, T.; Shirae, Y.; Sasai, Y.; Sakamoto, M.; Fujita, T. J. Org. Chem. 2006 , 71 ,

6834–6839; (b) Mino, T.; Shindo, H.; Kaneda, T.; Koizumi, T.; Kasashima, Y.;

Sakamoto, M.; Fujita, T. Tetrahedron Lett. 2009 , 50 , 5358–5360; (c) Mino, T.;

Shibuya, M.; Suzuki, S.; Hirai, K.; Sakamoto, M.; Fujita, T. Tetrahedron 2012 , 68 ,

429–432; (d) Mino, T.; Watanabe, K.; Abe, T.; Kogure, T.; Sakamoto, M.

Heterocycles 2013 , 87 , 2015–2021.

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12. (a) Mino, T.; Kajiwara, K.; Shirae, Y.; Sakamoto, M.; Fujita, T. Synlett 2008 ,

2711–2715; (b) Mino, T.; Koizumi, T.; Suzuki, S.; Hirai, K.; Kajiwara, K.;

Sakamoto, M.; Fujita, T. Eur. J. Org. Chem. 2012 , 678–680; (c) Mino, T.; Kogure,

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1505.

13. General procedure of palladium-catalyzed decarboxylative coupling of benzoic acid

derivatives with arylboroxins: To a mixture of arylcarboxylic acid (0.20 mmol),

Ag₂CO₃(165 mg, 0.60 mmol), Pd(TFA)₂(5.0 mg, 0.015 mmol, 7.5 mol %), and

ligand 1d (4.0 mg, 0.015 mmol, 7.5 mol %) in DMSO (1.0 mL) was added

arylboroxin (0.40 mmol) at room temperature under an atmosphere of air.

After the mixture was stirred at 80 °C for 2 h, the mixture was diluted with

ethyl acetate and water. The organic layer was washed with brine, dried over

MgSO₄, and concentrated under reduced pressure. The residue was puriﬁed by

silica gel chromatography (hexane/EtOAc = 20:1).

14. General procedure of palladium-catalyzed decarboxylative coupling of benzoic acid

derivatives with aryl(trialkoxy)silanes: To

a mixture of aryl(trialkoxy)silane

(0.20 mmol), AgF (76.6 mg, 0.60 mmol), Pd(TFA)₂(5.0 mg, 0.015 mmol,

7.5 mol %), and ligand 1g (6.7 mg, 0.015 mmol, 7.5 mol %) in DMAc (1.0 mL)

was added arylcarboxylic acid (0.40 mmol) at room temperature under an

atmosphere of air. After the mixture was stirred at 100 or 110 °C for 2–8 h, the

mixture was diluted with ethyl acetate and water. The organic layer was

washed with brine, dried over MgSO₄, and concentrated under reduced

pressure. The residue was puriﬁed by silica gel chromatography (hexane/

EtOAc = 20:1).

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Article Doi

Palladium-catalyzed decarboxylative coupling of benzoic acid derivatives using hydrazone ligands

DOI: 10.1016/j.tetlet.2014.04.017

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Article abstract of DOI:10.1016/j.tetlet.2014.04.017

Full text of DOI:10.1016/j.tetlet.2014.04.017

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