An Efficient Metal-Catalyzed Hydroalkylation

Abstract

An efficient metal-catalyzed hydroalkylation of various styrenes, norbornene, and cyclohexadiene with 1,3-dicarbonyl compounds has been developed. This new bismuth-catalyzed C-H functionalization provides the corresponding alkylated pentanediones in good to excellent isolated yields after short reaction times.

Key words

hydroalkylation - hydroarylation - benzylation - bismuth - C-H activation - catalysis - styrene - alkene

References and Notes

• For reviews, see:
• 1a Dyker G. Angew. Chem. Int. Ed.  1999,  38:  1699 
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• 3 Rueping M. Nachtsheim BJ. Kuenkel A. Org. Lett.  2007,  9:  825 
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• 5a Pei T. Widenhoefer RA. J. Am. Chem. Soc.  2001,  123:  11290 
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• 5d Widenhoefer RA. Pure Appl. Chem.  2004,  76:  671 
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8

1,3-Diarylbut-1-enes were observed as the major byproducts.

10

Typical Procedure: Preparation of 3-[1-(4-fluoro-phenyl)ethyl]pentane-2,4-dione (3f)
A two-necked round-bottom flask charged with Bi(OTf)₃ (H₂O)₄ (0.036 g, 0.05 mmol) and 2,4-pentanedione (400 mg, 4 mmol) dissolved in MeNO₂ (3 mL) was heated to 100 °C. 4-Fluorostyrene (1 mmol) dissolved in 1 mL of MeNO₂ was added dropwise via syringe for 4 h and stirred at this temperature for 1 h. After cooling the reaction mixture to r.t. the crude reaction mixture was directly purified by column chromatography on silica gel (hexane-EtOAc, 10:1) to give 198 mg (89%) of the product as a pale yellow oil which solidified upon standing. ¹H NMR (250 MHz, CDCl₃): δ = 7.19-7.09 (m, 2 H, ArH), 7.03-6.91 (m, 2 H, ArH), 3.97 (d, J = 11.3 Hz, 1 H, CH), 3.58 (dq, J = 11.3, 6.9 Hz, 1 H, CH), 2.25 (s, 3 H, CH₃), 1.84 (s, 3 H, CH₃) 1.18 (d, J = 6.9 Hz, 3 H, CH₃). ¹³C NMR (63 MHz, CDCl₃): δ = 203.8, 203.7, 162.2 (d, J = 245.4 Hz), 139.4 (d, J = 3.4 Hz), 129.4 (d, J = 7.9 Hz), 116.24 (d, J = 21.3 Hz), 77.4, 40.2, 30.4, 30.2, 21.5. IR (neat): ν = 3441, 3260, 2925, 2845, 1647, 1385, 1076, 698, 466 cm^-1. ESI-MS: m/z (%) = 240.0(100) [M + NH₄]⁺. Anal. Calcd for C₁₃H₁₅FO₂: C, 70.25; H, 6.80. Found: C, 70.53; H, 6.76.

11

Spectroscopic Data for 3-[1-(2-fluorophenyl)eth-yl]pentane-2,4-dione (3g) ¹H NMR (250 MHz, CDCl₃): δ = 7.34-6.95 (m, 4 H, ArH), 4.24 (d, J = 11.3 Hz, 1 H, CH), 3.89 (dq, J = 11.3, 6.9 Hz, 1 H, CH), 2.28 (s, 3 H, CH₃), 1.94 (s, 3 H, CH₃) 1.23 (d, J = 6.9 Hz, 3 H, CH₃). ¹³C NMR (63 MHz, CDCl₃): δ = 203.13, 202.98, 160.5 (d, J = 245.7 Hz), 129.7 (d, J = 14.0 Hz), 129.2 (d, J = 4.9 Hz), 128.6 (d, J = 8.4 Hz), 124.5 (d, J = 3.5 Hz), 116.0 (d, J = 22.6 Hz), 74.86, 34.6, 30.2, 28.9, 19.48. IR (neat): ν = 3441, 2980, 1699, 1493, 1452, 1360, 1281, 1228, 1246, 761 cm^-1. ESI-MS: m/z (%) = 239.9 (100) [M + NH₄]⁺, 462.3 (90) [2 M + NH₄]⁺. Anal. Calcd for C₁₃H₁₅FO₂: C, 70.25; H, 6.80. Found: C, 70.51; H, 6.78.