Trans-Cinnamaldehyde [1] (Aldrich, distilled before use).
Triphenylphosphine (Aldrich).
Methyl iodide (Aldrich).
Tetrahydrofuran (dry, inhibitor-free, obtained by passage through an Anhydrous Engineering drying column).
Sodium hexamethyldisilazane (Aldrich, 1.6M in THF).
Solvents for extraction and chromatography were technical grade.

(a) Formation of Methyltriphenylphosphonium iodide [2]. To a solution of triphenylphosphine (26.2g, 100 mmol) in THF (100 mL), was added methyl iodide (6.23 mL, 100 mmol). After approximately three hours, a white precipitate formed which was filtered, washed with cold THF and dried in air to give methyltriphenylphosphonium iodide [2] as a fine white crystalline solid (30.1 g, 84.3 mmol, 84 %). (b) Formation of trans-1-Phenylbuta-1,3-diene [3]. Under an inert atmosphere, a solution of methyltriphenylphosphonium iodide [2] (12.9 g, 36 mmol) in dry THF (50 mL) was cooled to 0^oC. Sodium hexamethyldisilazane (1.6 M in THF, 22.5 mL, 36 mmol) was added dropwise with vigorous stirring. After approximately twenty minutes a clear solution was formed to which trans-cinnamaldehyde [1] (3.78 mL, 30 mmol) was added dropwise with vigourous stirring. Once the addition of [1] was complete, the reaction was allowed to warm to room temperature. Once all starting material was consumed (as observed by TLC; eluting with 1 % Et₂O in pentane, on silica) the reaction was filtered through a pad of silica and concentrated ‘in vacuo’. Purification by column chromatography (eluting with 1 % Et₂O in pentane, on silica) and Kugelrohr distillation (70^oC at 5 mm/Hg) gave trans-1-phenylbut-1,4-diene [3] as a colourless oil (3.47 g, 26.7 mmol, 89 %).

Acknowledgement and thanks are made to Dr. M. Paz Munoz, University of Bristol, for essential input and support. The methyltriphenylphosphonium salt [2] can be formed with either methyliodide or methylbromide; the counterion having no effect on the yield of the Wittig reaction. Due to the volatile nature of the trans-phenylbutadiene product, it is important to avoid high vacuum or high temperature when concentrating solutions. Manipulations involving air-sensitive materials were carried out on a vacuum line under nitrogen, employing standard Schlenk techniques. The above procedure can be applied to other commercially available trans-cinnamaldehyde derivatives; for example, the p-methoxy-trans-cinnamaldehyde was synthesised via the above method to give the trans-1-(p-methoxy)phenylbuta-1,3-diene in 98 % yield.

¹H NMR (CDCl₃, 300 MHz): 5.17 (d, ¹H, ³JHH = 10.0 Hz, C[4]Htrans); 5.33 (d, 1H, ³JHH = 16.8 Hz, C[4]Hcis); 6.49 (dt, 1H, ³JHH = 10.2 Hz, 16.8 Hz, C[3]H); 6.57 (d, 1H, ³JHH = 15.8 Hz, C[1]H); 6.79 (dd, 1H, ³JHH = 16.8 Hz, 10.0 Hz, C[2]H), 7.24 (m, 2H, CHo-arom); 7.33 (m, 2H, CHm-arom); 7.41 (m, 1H, CHp-arom). ¹³C NMR (CDCl₃, 300 MHz):117.6 (C[4]H2); 126.4 (CHm-arom); 127.6 (CHp-arom); 128.6 (CHo-arom); 129.6 (C[2]H); 132.8 (C[1]H); 137.0 (Ci-arom); 137.2 (C[3]H).

H. Lebel, V. Paquet, J. Am. Chem. Soc., 2004, 126, 320 – 328.

i) H. Lebel, V. Paquet, C. Proulx, Angew. Chem. Int. Ed., 2001, 40, 2887 – 2890. ii) K. Kobayashi, S. Oka, T. Okamoto, S. Tanimoto, J. Org. Chem., 1988, 53, 4897 – 4901.