[Cl:1][C:2]1[C:11]2[C:6](=[CH:7][CH:8]=[CH:9][CH:10]=2)[O:5][CH:4]([C:12]2[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=2)[C:3]=1[CH:18]=[N:19]O.C1(P(C2C=CC=CC=2)C2C=CC=CC=2)C=CC=CC=1.C(N(CC)CC)C>ClCCCl.C(Cl)(Cl)(Cl)Cl>[Cl:1][C:2]1[C:11]2[C:6](=[CH:7][CH:8]=[CH:9][CH:10]=2)[O:5][CH:4]([C:12]2[CH:13]=[CH:14][CH:15]=[CH:16][CH:17]=2)[C:3]=1[C:18]#[N:19]A solution of 25.7 g 4-chloro-3-hydroxyiminomethyl-flav-3-ene and 28.3 g triphenylphosphine in 250 ml 1,2-dichloroethane and 8.7 ml carbon tetrachloride is heated at 60° C. To this solution one adds 12.54 ml triethylamine. The temperature is maintained between 62°-65° C. during the addition and for further 25 minutes. The mixture is cooled to 0° C., filtered and evaporated. The crude material is extracted with hexane. The combined extracts are evaporated and purified by column chromatography on silicagel using a mixture of dichloromethane and hexane as eluant. The pure fraction is evaporated and crystallized in diisopropylether. Pure 4-chloro-3-cyano-flav-3-ene is obtained as pale yellow crystalls; m.p. 99° C.
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