Triethylamine (0.65ml, 4.7mmol) was added to 8-^tbutyldimethylsilyloxy-oct-4(E)-enoic acid (16) (0.58g, 2.1mmol) in dry diethyl ether (80ml) at 0degC under argon. After stirring for 15min. ethyl chloroformate (0.25ml, 2.6mmol) was added to the reaction mixture and the mixture stirred for a further 1h at 0degC. Triethylamine hydrochloride was removed by filtration and the residue concentrated. Filtration through a silica pad gave the crude mixed anhydride as a clear liquid (0.57g, 81%).

¹H nmr (300MHz, CDCl3) delta 5.53-5.34 (2H, m, CH=CH), 4.25 (2H, q, J = 7.2 Hz, CH2CH3), 3.56 (2H, t, J = 6.4 Hz, CH2OSi), 2.48 (2H, t, J = 6.5 Hz, CH2CO2), 2.33 (2H, dt, J = 6.9, 6.5 Hz, CH2CH2CO2), 2.02 (2H, dt, J = 6.9, 6.5 Hz, CH2CH), 1.55 (2H, m, -CH2-), 1.34 (3H, t, J = 7.2 Hz, CH2CH3), 0.87 (9H, s, C(CH3)3), 0.02 (6H, s, Si(CH3)2); Vmax (neat) 2954, 2929, 2856, 1823, 1761, 1667, 1548, 1472, 1413, 1389 cm^-1.

This material (0.22g, 0.67mmol) in dry tetrahydrofuran (1ml) was immediately added to a solution of (4S )-benzyl-2-oxazolidinone (0.13g, 0.75mmol) in dry tetrahydrofuran (3ml) at -78degC under an argon atmosphere, that had been pretreated with sodium hexamethyldisilazide (0.75ml of a 1.0M solution in tetrahydrofuran, 0.75mmol) for 1h at -78degC, and the reaction stirred at -78degC for a further 2h. Sodium hexamethyldisilazide (0.75ml of a 1.0M solution in tetrahydrofuran, 0.75mmol) was then added to the reaction mixture and after a further 30min methyl iodide (0.05ml, 0.81mmol) was added and the reaction stirred until complete. The reaction was quenched with saturated aqueous ammonium chloride (1ml) and the solvent removed under reduced pressure. The resultant slurry was diluted with ethyl acetate (50ml) and successively washed with saturated aqueous sodium bicarbonate (20ml) and saturated aqueous sodium chloride (20ml). After drying the solvent was evaporated and the crude product purified by chromatography on silica gel (ethyl acetate-cyclohexane, 1:20, v/v). (4S, 2'S, 4'E)-3-(8'-^tbutyldimethylsilyloxy-2'-methyl-oct-4'-enoyl)-4-benzyl-2-xazolidinone (17) was obtained as a clear viscous oil as the predominant diastereoisomer (90mg, 30%, > 96 % d.e. by 300 MHz nmr), [alpha]D = +56deg (c = 1.0, CDCl3).

Proton nmr (300MHz, CDCl3) delta 7.34-7.18 (5H, m, ArH), 5.49-5.33 (2H, m, CH=CH), 4.66-4.61 (1H, m, NCH), 4.15(2H, m, CH2O), 3.73 (1H, m, CHCH3), 3.56 (2H, t, J = 6.5 Hz, CH2OSi), 3.25 (1H, dd, J = 13.3, 3.2 Hz, CHaHbPh), 2.74 (1H, dd, J = 13.3, 9.6 Hz, CHaHbPh), 2.36 (1H, m, CHaHbCHCH3), 2.08 (1H, m, CHaHbCHCH3), 2.00 (2H, dt, J = 6.9, 6.5 Hz, CH2CH), 1.53 (2H, m, -CH2-), 1.18 (3H, d, J = 6.9 Hz, CHCH3), 0.86 (9H, s, C(CH3)3), 0.01 (6H, s, Si(CH3)2); Vmax (neat) 3088, 3064, 3029, 2953, 2929, 2856, 1784, 1699, 1498, 1472, 1462, 1455, 1386 cm^-1; m/z (CI, NH3) 463 (M+NH4)⁺, 446 (M+H)⁺, 388, 228, 211, 195, 178, 132, 108, 91, 78. Found (M+NH4)⁺ 463.2976. C25H43O4N2Si requires 463.2992.

Preparation of (2S, 4E)-8-^tButyldimethylsilyloxy-2-methyl-oct-4-enoic acid (18)

Potassium hydroxide (23mg, 0.41mmol) in water (0.5ml) was added to (4S, 2'S, 4'E)-3-(8'-^tbutyldimethylsilyloxy-2'-methyl-oct-4'-enoyl)-4-benzyl-2-xazolidinone (17) (65mg, 0.15mmol) in methanol / tetrahydrofuran (2ml, 1:1, v/v) and stirred at room temperature for 10h. The solvent was removed under reduced pressure and the residue acidified to pH 1 with 1M hydrochloric acid at < 0degC. The liberated acid was extracted with ethyl acetate (5x1ml) and the organics combined and washed with saturated aqueous sodium chloride (3ml). The organics were dried and concentrated to yield the crude acid which was purified by chromatography on silica gel (ethyl acetate-cyclohexane, 1:20, v/v) to give (2S, 4E)-8-^tbutyldimethylsilyloxy-2-methyl-oct-4-enoic acid (18) as a colourless liquid (35mg, 84%), [alpha]D = +4deg (c = 1.0, CDCl3)

Proton nmr (300MHz, CDCl3) delta 5.49-5.32 (2H, m, CH=CH), 3.57 (2H, t, J = 6.5 Hz, CH2OSi), 2.47 (1H, m, CHCH3), 2.34 (1H, m, CHaHbCHCH3), 2.10 (1H, m, CHaHbCHCH3), 2.01 (2H, dt, J = 6.8, 6.6 Hz, CH2CH), 1.54 (2H, m, -CH2-), 1.14 (3H, d, J = 6.9 Hz, CHCH3), 0.87 (9H, s, C(CH3)3), 0.02 (6H, s, Si(CH3)2); Vmax (neat) 3305 br, 2929, 2857, 1738, 1709, 1548, 1463 cm^-1; m/z (CI, NH3) 287 (M+H)⁺, 279, 225, 155, 137, 121, 94, 72. Found (M+H)⁺ 287.2059. C15H31O3Si requires 287.2042.