A solution of n-butyl lithium (2.69 g) in hexane (26.25 ml) was added dropwise to a stirred solution of 2-oxopropylidenetriphenylphosphorane (12.73 g) in anhydrous tetrahydrofuran (400 ml) at -65° C. in an atmosphere of dry nitrogen. The red solution was stirred at -65° C. for a further 15 minutes and was then treated with a solution of 2-phenoxyethyl bromide (8.04 g) in anhydrous tetrahydrofuran (40 ml). The mixture was stirred at 0° C. for one hour and then at ambient temperature for 2 hours, and was poured into water and extracted with diethyl ether. The organic solution was washed with water then dried over magnesium sulphate. Evaporation of the solution gave a yellow gum which slowly hardened on prolonged storage after trituration with diethyl ether to give crude 2-oxo-5-phenoxypentylidenetriphenylphosphorane (8.0 g), m.p. 83°-89° C. [elemental analysis: P, 7.4%; C29H27O2P requires P, 7.1%. νmax 715, 755, 1110, 1400, 1445, 1490 and 1555 cm-1. NMR (approximately 10% w/v solution in deuterochloroform): multiplets at 6.7-7.9δ and 1.8-2.7δ, triplet at 4.0δ (J=6 cycles/second)].
