Rearrangement of bicyclo[2.2.1]heptane ring systems by titanocene alkylidene complexes to bicyclo[3.2.0]heptane enol ethers. Total synthesis of (±)-Δ^(9(12))-capnellene

摘要: A variety of ester-substituted norbornenes react with titanamethylene complex (Tebbe's reagent) to yield stable titanacyclobutanes. Endo esters do not the reagent in competition norbornene double bond. The X-ray structure metallacycle formed from titanacene methylene and 1-methylbicyclo[2.2.l]hept-5-ene-2,3-dicarboxylic acid diisopropyl ester was determined. On heating, rearranged to a carbene-olefin complex. The ratio productive opening, cleavage bicycloheptane ring system, to nonproductive regeneration starting materials, is controlled by steric factors that were studied analyzed. opening detected formation product resulting from the intramolecular trapping intermediate titanium alkylidene endo functionality Wittig-like reaction substituted bicyclo[3.2.0]heptenes. Rearrangement titanacycle 4,4-dimethyltricyclo[ 5.2.1.0^(1,5)]dec-8-ene-6-carboxylic tert-butyl yielded 10,10-dimethyl-3-methoxy-7- vinyltricyclo[5.3.0.0^(2,5)]dec-2-ene, which transformed into Δ ^(9(12))-capnellene good yield.