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

摘要

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 (3b_2)) to the "heptamer" (3b_7,a pentadecaene).Oligoenes 3b_2,3b_3,3b_4,3b_5,and 3b_7 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 3b_2,3b_4,and 3b_6 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 3b_2.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.