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Synlett 2008(17): 2711-2715  
DOI: 10.1055/s-0028-1083381
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Room-Temperature Palladium-Catalyzed Allyl Cross-Coupling Reaction with Boronic Acids Using Phosphine-Free Hydrazone Ligands

Takashi Mino*, Kenji Kajiwara, Yoshiaki Shirae, Masami Sakamoto, Tsutomu Fujita
Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho,Inage-ku, Chiba 263-8522, Japan
Fax: +81(43)2903401; e-Mail: tmino@faculty.chiba-u.jp;
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Publication History

Received 3 July 2008
Publication Date:
01 October 2008 (online)

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Abstract

Palladium-catalyzed allyl cross-coupling reaction of allylic acetates with a variety of boronic acids at room temperature using a catalytic amount of Pd(OAc)2 with phosphine-free hydrazone as a ligand gave the allylbenzene derivatives in good yields.

Key words

palladium - catalysis - allyl cross-coupling - boronic ­acid - hydrazones

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General Procedure for Allyl Cross-Coupling Reaction of Cinnamyl and Allyl Acetate with Boronic Acids (Table 2): To a mixture of acetate (0.5 mmol), K2CO3 (138.2 mg, 1.0 mmol), Pd(OAc)2 (2.24 mg, 0.01 mmol), and ligand 1c (2.22 mg, 0.01 mmol) in DMF (1.5 mL) and H2O (0.5 mL) was added boronic acid (0.6 mmol) at r.t. under an atmosphere of argon. After 1 h, the mixture was diluted with EtOAc and H2O. The organic layer was washed with brine, dried over MgSO4, and concentrated under reduced pressure. The residue was purified by silica gel chromatography. All prepared compounds 3 (except for 3e) were known and identified by ¹H NMR, ¹³C NMR, and MS. Analytical Data of 3e (Table 2, entry 7): colorless oil. IR (neat): 1604 cm-¹. ¹H NMR (CDCl3): δ = 2.29 (s, 6 H), 3.47 (d, J = 6.5 Hz, 2 H), 6.33 (dt, J = 15.7, 6.6 Hz, 1 H), 6.45 (d, J = 15.9 Hz, 1 H), 6.86 (s, 3 H), 7.16-7.37 (m, 5 H). ¹³C NMR (CDCl3):
δ = 21.1, 39.2, 126.1, 126.4, 127.0, 127.8, 128.5, 129.4, 130.8, 137.5, 138.0, 140.0. MS (EI, relative intensity): m/z = 222 (86) [M+]. HRMS (FAB-MS): m/z calcd for C17H18: 222.1409; found: 222.1408. GC-MS purity: 98.5%.

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Preparation of Hydrazone 2b: To a solution of N-aminopiperidine (0.060 g, 0.60 mmol) in MeOH (2.0 mL) was added 2-pyridinecarboxaldehyde (0.054 g, 0.51 mmol) and the mixture was stirred for 24 h at r.t. The mixture was directly concentrated under reduced pressure. The residue was purified by silica gel chromatography (hexane-EtOAc, 4:1). Yield: 0.092 g, 0.49 mmol, 96%; colorless oil. IR (neat): 1572 cm-¹. ¹H NMR (CDCl3): δ = 1.51-1.59 (m, 2 H), 1.66-1.79 (m, 4 H), 3.24 (t, J = 5.6 Hz, 4 H), 7.08-7.12 (m, 1 H), 7.59-7.64 (m, 2 H), 7.83 (dd, J = 8.1, 0.8 Hz, 1 H), 8.50 (dd, J = 4.8, 0.8 Hz, 1 H). ¹³C NMR (CDCl3): δ = 24.4, 25.4, 52.0, 119.4, 122.3, 134.3, 136.5, 149.4, 156.3. MS (EI, relative intensity): m/z = 189 (11) [M+]. HRMS (FAB-MS): m/z calcd for C11H15N3: 189.1266; found: 189.1280.

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General Procedure for Allyl Cross-Coupling Reaction of Disubstituted Allylic Acetates with 1-Naphthalene- boronic Acid (Table 3): To a mixture of acetate (0.5 mmol), Cs2CO3 (423.6 mg, 1.3 mmol), Pd(OAc)2 (5.61 mg, 0.025 mmol), and ligand 2a (5.08 mg, 0.025 mmol) in MeCN (2 mL) was added 1-naphthaleneboronic acid (103.2 mg, 0.6 mmol) at r.t. under an atmosphere of argon. After 24 h, the mixture was diluted with EtOAc and H2O. The organic layer was washed with brine, dried over MgSO4, and concentrated under reduced pressure. The residue was purified by silica gel chromatography. Compounds 3m and 3n were known and identified by ¹H NMR, ¹³C NMR, and MS.