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Synthesis of Oligoenes that Contain up to 15 Double Bonds from 1,6-Heptadiynes

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posted on 27.12.2006, 00:00 by Constantin Czekelius, Jillian Hafer, Zachary J. Tonzetich, Richard R. Schrock, Ronald L. Christensen, Peter Müller
This paper reports the synthesis of polyene oligomers (“oligoenes”) that contain up to 15 double bonds that are identical to the “all five-membered ring” species formed through cyclopolymerization of diisopropyldipropargylmalonate. The oligoenes contain an isopropylidene unit at each end. The isolated oligoenes range from the “dimer” (a pentaene, (E)-di-1,2-[1-(2-methyl-propenyl)-4,4-di-iso-propyl-carboxy-cyclopent-1-enyl]-ethene (3b2)) to the “heptamer” (3b7, a pentadecaene). Oligoenes 3b2, 3b3, 3b4, 3b5, and 3b7 were prepared through Wittig-like reactions between aldehydes and the appropriate monometallic Mo alkylidene or bimetallic Mo bisalkylidene species whose alkylidene is derived from an identical five-membered ring monomeric unit. Compounds 3b2, 3b4, and 3b6 were prepared through McMurry coupling reactions of aldehydes. A representative aldehyde (the “monomeric” aldehyde) is diisopropyl-3-formyl-4-(2-methylprop-1-enyl)cyclopent-3-ene-1,1-dicarboxylate (2b), McMurry coupling of which yields 3b2. A heptaene that contains a six-membered ring in the central unit also was prepared in a Wittig-like reaction involving a bimetallic Mo alkylidene; this species is a model for oligoenes that contain both six-membered and five-membered rings. X-ray structures of two bimetallic species that are employed in the synthesis of the oligoenes are reported.