33 g (72.1 mmoles) of [2-(1,3-dioxan-2-yl)ethyl] triphenylphosphonium bromide are suspended in 100 ml of THF. The suspension is cooled to 0° C. and 8.5 g (75.6 mmoles) of potassium terbutylate are added in small amounts. The mixture is left to stand until its temperature reaches 20° C. It is then stirred for 1 hour at which point it is cooled to 0° C. There is then slowly added a solution of 3-(1-adamantyl)-4-tert.butyl-dimethylsilyloxybenzaldehyde in 100 ml of TMF. Once the addition has ended, the mixture is left to stand until its temperature reaches ambient temperature at which point it is stirred for 2 hours, then poured into water, and extracted with methylene chloride. The organic phase is decanted, washed with water, dried over MgSO4 and the solvents evaporated. The residue is purified by passage through a silica column (eluant: 50:50 mixture of CH2Cl2 and hexane), yielding 19.4 g (95% yield) of the expected mixture containing more than 90% of isomer Z, and less than 10% of isomer E.
