INSECT SEX PHEROMONES: TRANSITION METAL-CATALYZED STEREOSELECTIVE SYNTHESES OF INTERNAL CONJUGATED (E)-ENYNES

Abstract

Functionalized (E)-l,3-enynes of general formula 1 have been prepared by coupling reaction of or-functionalized 1-alkynes with molar excesses of stereo-isomerie mixtures of 1-bromo-l-alkenes, in the presence of a catalyticamount of (PPh3)4 Pd and CuJ. The reactions were carried out under phase transfer conditions employing benzyltriethylammonium chloride as phase transfer agent, benzene as organic solvent and diluted aq NaOH as base. Using this procedure (E)-13–hexadecen-11-yn-l-ol (2) and (E)-11-tetradecen-9-yn-l-ol (3) were obtained in good yield and high stereoisomeric purity (95 ± 97%). Such compounds were purified from the corresponding (Z)-stereoisomers by crystallization from hexane at low temperature. Stereoisomeric mixtures of 1-bromo-l-alkenes, which were used as starting materials in these coupling reactions, have been prepared by reaction of 1,2-dibromoalkanes with powdered KOH in a hydrocarbon solvent, in the presence of Aliquat 336. Functionalized (E)-l,3-enynes of general formula 1 have also been prepared in high yield by selective linear codimerization of π-functionalyzed 1-alkynes with 1,3-butadiene in the presence of a catalytic amount of dihydridotetrakis(tributylphosphine)ruthenium. Such enynes, e.g. (E)-9-dodecen-7-yn-l-yl acetate (16) and (E)-11-tetradecen-9-yn-1-yl acetate (8) had high stereoisomeric purity (ca. 99%), but contained ca. 3% of the corresponding (E)-1,4-enyne isomers.