Saturated N-Heterocyclic Carbene Oxime and Amine Palladacycle Catalysis of the Mizoroki-Heck and the Suzuki Reactions [1]

Abstract

ortho-Palladated aryl oxime and amines with a N-heterocyclic carbene ligand show increased thermal stability and catalyze the Mizoroki-Heck and Suzuki reaction with high yields, and moderate TON (2,000-92,000) and TOF (200-4,300 h^-1). Homo coupling of the aryl halides gave low yields of the biaryls in the presence of these catalysts.

Key words

saturated N-heterocyclic carbene - oxime and amine palladacycle - Mizoroki-Heck reaction - Suzuki reaction - biaryl

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NCL Communication No.: 6643

References

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• 6 Alonson DA. Najera C. Pacheco MC. Org. Lett.  2000,  2:  1823 
• 8 Iyer S. Jayanthi A. Tetrahedron Lett.  2001,  42:  7877 
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NCL Communication No.: 6643

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Iyer, S.; Jayanthi, A.; Kulkarni, G. M.; Subramanyam, S.; Kashinath, D. K., unpublished results from our research group.

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All compounds reported are known and were characterized by spectroscopic methods
(a) Mizoroki-Heck reaction with benzophenone oxime carbene palladacycle (Cat 3) : To 5.175 g (25 mmol) of 1-bromonaphthalene, styrene (3.03 g, 30 mmol) and 25 mL N-methylpyrrolidinone were added to, followed by 2.49 g (30 mmol) of NaOAc and 0.00022 g (0.0004 mmol) of the (Cat 3) benzophenone oxime palladacycle carbene catalyst. The reaction mixture was heated to 140-150 °C in an oil bath until the bromonaphthalene was completely consumed (36 h). HCl (10%, 100 mL) was added to the reaction mixture and extracted with ethyl acetate (3 × 100 mL). Washing the organic extracts with brine, drying over anhydrous Na₂SO₄, concentration on a rotary evaporator and purification by column chromatography (silica gel : 100-200 mesh) gave 5.32 g (92.6%, TON 61, 956) of E-1-naphthylstilbene.
(b) Suzuki coupling of bromobenzene with phenyl boronic acid catalyzed by carbene palladacycle (Cat - 2) : Bromobenzene (0.314 g, 2 mmol), phenyl boronic acid (0.367 g, 3 mmol), catalyst (3, 0.0004 g, 0.0007 mmol) and K₃PO₄ (0.920 g, 4.34 mmol) were dissolved in DMF (5 mL) and the reaction mixture heated to 120 °C for 24 h. The biphenyl product was isolated by addition of HCl (10%, 25 mL) and extracted with ethyl acetate followed by purification by column chromatography (silica gel : 100-200 mesh) in 73.3% (0.226 g, TON 2, 096) yield.
(c) Biaryl coupling catalyzed by carbene palladacycle (Cat - 2) and K₂CO₃. 2-Bromopyridine (0.158 g, 1.0 mmol), K₂CO₃ (0.165 g, 1.2 mmol), catalyst (2, 0.0017 g, 0.003 mmol) were dissolved in DMF (5 mL) and heated to 140 °C for 24 h. The bipyridyl was isolated by the usual extractive procedure with water and ethyl acetate. Purification by column chromatography (silica gel: 100-200 mesh) gave 0.025 g (16%) yield of the 2,2′-bipyridyl. ¹H NMR (δ, 200 MHz, CDCl₃) 8.69-8.71 (d, 2 H), 8.39-8.43 (d, 8 Hz, 2 H), 7.80-7.88 (m, 2 H), 7.27-7.36 (m, 2H).