High temperature Heck coupling of (2-bromo-5-methoxy-3-methylphenyl)-acetonitrile with ethyl acrylate.; 3-(2-cyanomethyl-4-methoxy-6-tolyl)-acrylic acid ethyl ester

lisa frost (kafs4@sussex.ac.uk),
A contribution from the Caddick Group, Sussex

Chemicals Used
(2-bromo-5-methoxy-3-methylphenyl)-acetonitrile [SyntheticPage 172] Palladium dichloride-bis-triphenylphosphine (Aldrich) Tri-o-tolylphosphine [SyntheticPage 170] Triethylamine (distilled from CaH₂) Ethyl acrylate (Lancaster) Toluene (distilled from sodium)

Procedure
In a high pressure vessel was placed 2-bromo-5-methoxy-3-methylphenyl)-acetonitrile (17.6 g, 73 mmol, 1 equiv), Pd(PPh₃)₂Cl₂ (2.57 g, 3.67 mmol, 5 mol%), P(o-tolyl)₃ (3.35 g, 11 mmol, 15 mol%), ethyl acrylate (8.8 g, 88 mmol, 1.2 equiv), triethylamine (11.1 g, 110 mol, 1.5 equiv) and toluene (22 mL/g nitrile). The vessel was purged with nitrogen, sealed and slowly cooled to -78 ^oC. The vessel was evacuated at this temperature, sealed and allowed to slowly warm to room temperature. The vessel was then heated to 165 ^oC for 16 h, after which it was allowed to cool to room temperature and was washed with water (200 mL). The organics were extracted into ether (3 x 200 mL)and washed with a further portion of water (100 mL). The combined organics were dried over MgSO₄, filtered and concentrated in vacuo. The resulting brown oil was purified by column chromatography on silica gel with petrol:ethyl acetate (5:1 v:v) as the eluent yielding the title compound as a yellow solid (9.0 g, 48%)

Author's Comments
The glass vessel used in this reaction was basically a schlenk tube (or ampule) fitted with a youngs tap. The tube was made from thick glass able to withstand moderate pressures. This reaction seems low yielding, but the yield can vary from 75% to 30% depending on i. catalyst purity, ii. turnover iii. reaction environment. The catalyst is easily poisoned in this reaction forming a palladium mirror on the vessel. If the temperature of the reaction is lowered the reaction does not take place. Further no SM is recovered. This reaction has been carried out on various scales (20g-0.1g) all yeilding around 60% of the required product.

Data
1H nmr (CDCl₃, 300 MHz) 7.52 (1H, d, J = 16.0 Hz), 6.69 (1H, d, J = 2.5 Hz), 6.55 (1H, d, J = 2.5 Hz), 5.81 (1H, d, J = 16.0 Hz), 4.08 (2H, q, J = 7.2 Hz), 3.63 (2H, s), 2.14 (3H, s), 1.15 (3H, t, J =7.2 Hz).

Lead Reference
Rucker, Mark; Brueckner, Reinhard; Syn.Lett.; 10; 1997; 1187-1189

Other References
Goerth, Felix Christian; Rucker, Mark; Eckhardt, Matthias; Brueckner, Reinhard; Eur.J.Org.Chem.; 14; 2000; 2605 - 2612.

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