Metallic Samarium Promoted Self-Coupling of Baylis-Hillman Adducts to Functionalized 1,5-Hexadienes in the Presence of the I₂/ClCO₂Et/BiCl₃ System

Abstract

A facile strategy for the self-coupling of Baylis-Hillman adducts to functionalized 1,5-hexadienes has been described. Promoted by the Sm/I₂/ClCO₂Et/BiCl₃ system, the present method allows for the conversion of MBH adducts to their corresponding 1,5-hexadienes.

Keywords

Baylis-Hillman adduct - metallic samarium - self-­coupling - functionalized 1,5-hexadiene - Lewis acid

References and Notes

• For reviews, see:
• 1a Ciganek E. Org. React.  1997,  51:  201 
• 1b Basavaiah D. Rao PD. Hyma RS. Tetrahedron  1996,  52:  8001 
• 1c Basavaiah D. Rao AJ. Satyanarayana T. Chem. Rev.  2003,  103:  811 
• 1d Singh V. Batra S. Tetrahedron  2008,  64:  4511 
• 1e Basavaiah D. Rao KV. Reddy RJ. Chem. Soc. Rev.  2007,  36:  1581 
• 2a Ramachandran PV. Madhi S. Bland-Berry L. Reddy MVR. O’Donnel MJ. J. Am. Chem. Soc.  2005,  127:  13450 
• 2b Basavaiah D. Roy S. Org. Lett.  2008,  10:  1819 
• 2c Declerck V. Toupet L. Martinez J. Lamaty F. J. Org. Chem.  2009,  74:  2004 
• 2d Singh V. Saxena R. Batra S. J. Org. Chem.  2005,  70:  353 
• 2e Shi YL. Shi M. Chem. Eur. J.  2006,  12:  3374 
• For selected examples, see:
• 3a Radha Krishna P. Nasingam M. Kannan V. Tetrahedron Lett.  2004,  45:  4773 
• 3b Rodgen SA. Schaus SE. Angew. Chem. Int. Ed.  2006,  45:  3913 
• 3c Reddy LR. Fournier JF. Reddy BVS. Corey EJ. Org. Lett.  2005,  7:  2699 
• 3d Trost BM. Machacek MR. Tsui HC. J. Am. Chem. Soc.  2005,  127:  7014 
• 3e Konig CM. Harms K. Koert U. Org. Lett.  2007,  9:  4777 
• 3f Trost BM. Thiel OR. Tsui HC.
  J. Am. Chem. Soc.  2003,  125:  13155 
• 3g Lee S. Hwang GS. Shin SC. Lee TG. Jo RH. Ryu DH. Org. Lett.  2007,  9:  5087 
• 4 Li SY. Li J. Jia XS. Synlett  2007,  1115 
• 5 Zhao PC. Li J. Jia XS. Synlett  2008,  932 
• 6 Li J. Qian WX. Zhang YM. Tetrahedron  2004,  60:  5793 
• 7 For review, see: Banik BK. Eur. J. Org. Chem.  2002,  2431 

8

The stereochemistry of products 2 is all E, and the ^¹H NMR spectra and the melting points of 2 were well in coincidence with the reported ones.⁶

9

All new compounds were characterized by ^¹H NMR, ^¹³C NMR, elemental analysis, and IR spectroscopy.
General Procedure for the Synthesis of 1,5-Hexadiene 2
To a stirred solution of Sm powder (1.5 mmol) and ClCO₂Et (2 mmol) in THF (15 mL), BiCl₃ (5 mol%), I₂ (5 mol%), and Baylis-Hillman adduct 1 (1 mmol) were added. The resulting mixture was then allowed to reflux in the air. Until completion of the reaction, 3 mL HCl (1 M) was then added to quench the reaction, and the mixture was successively exacted with EtOAc (2 × 20 mL). The organic phase was washed with sat. brine (15 mL), dried over anhyd Na₂SO₄, filtered. The solvent was removed under reduced pressure to give the crude products, which were purified by column chromatography using EtOAc and PE (1:20) as eluent.
Selected Spectroscopic Data of Product 2
Compound 2d: white solid, mp 171.8-172.3 ˚C. IR (KBr): 1705, 1629, 1436 cm^-¹. ^¹H NMR (500 MHz, CDCl₃): δ = 7.99 (s, 2 H), 7.70 (s, 2 H), 7.46-7.39 (m, 8 H), 3.78 (s, 6 H), 2.83 (s, 2 H), 1.33 (s, 18 H) ppm. ^¹³C NMR (125 MHz, CDCl₃): d = 169.1, 151.8, 140.4, 132.7, 131.4, 129.6, 125.5, 52.1, 31.4, 27.0 ppm. MS: m/z (%) = 462 (10) [M⁺], 371 (17), 175 (100). Anal. Calcd for C₃₀H₃₈O₄: C, 77.89; H, 8.28. Found C, 77.78; H, 8.19.
Compound 2e: white solid, mp 168.6-169.0 ˚C. IR (KBr): 1707, 1560, 1432 cm^-¹. ^¹H NMR (500 MHz, CDCl₃): δ = 7.67 (s, 2 H), 7.60-7.17 (m, 8 H), 3.69 (s, 6 H), 2.58 (s, 4 H) ppm. ^¹³C NMR (125 MHz, CDCl₃): δ = 167.9, 139.9, 136.2, 133.6, 132.8, 130.4, 129.7, 127.3, 124.1, 52.1, 27.0 ppm. MS: m/z (%) = 508 (6) [M⁺], 397 (52), 174 (70), 115 (100). Anal. Calcd for C₂₂H₂₀Br₂O₄: C, 51.99; H, 3.97. Found C, 52.08; H, 3.83.