603-35-0

352-11-4

3462-95-1

General method: As an example of the synthesis of trans-3a: A mixture of 4.0 g (2.78 mmol) of 4-fluorobenzyl chloride and 8.73 g (3.30 mmol) of triphenylphosphine in 12 mL of benzene was refluxed for 48 h to give a white solid. The solid was collected by filtration to give (4-fluorobenzyl)triphenylphosphonium chloride in 82% yield. Then, a mixture of 9.97 g (2.5 mmol) of the above phosphonium salt, 2.37 g (2.2 mmol) of benzaldehyde, and 0.82 g (3.11 mmol) of 18-crown-6 in 56 mL of dichloromethane was stirred vigorously and 27 mL of aqueous 50 % K2CO3 was added slowly. After the addition was completed, the reaction mixture was stirred at room temperature for 72 hours. Upon completion of the reaction, the mixture was poured into water and extracted three times with ethyl acetate. The organic layers were combined and dried with anhydrous MgSO4. The organic solvent was removed by concentration under reduced pressure and the residue was purified by silica gel column chromatography (eluent: ethyl acetate/hexane = 1:10) to give a mixture of cis and trans-3a in 95.1% yield. The above mixture was refluxed with a catalytic amount of iodine in benzene for 3 h. After completion of the reaction, the mixture was purified by silica gel column chromatography (eluent: ethyl acetate/hexane=1:10) to afford trans-3a in 92% yield.