ASYMMETRIC-SYNTHESIS AND METALATION OF C2-SYMMETRICAL ANNULATED BICYCLOOCTYLCYCLOPENTADIENES

The cyclopentadienes (+)-(1R,7R,8R,10R)-8,10-diisopropyltricyclo[5.2.2.0(2,6)]undeca-2,5-diene (1a) and (-)-(1S,7S,8R,10R)-8,10-dimethyltricyclo[5.2.2.0(2,6)]undeca-2,5-diene (1b), abbreviated dialkyl-BCO-Cp, are chiral ligands possessing C2 symmetry. These dienes are efficiently prepared in five steps via (1) Birch reduced of 1,4-dialkylbenzene, (2) asymmetric dihydroboration-oxidation using enantiomerically pure isopinocamphenylborane, (3) bis(methanesulfonate) formation, (4) bisalkylation of cyclopentadiene to form spiro-annulated cyclopentadiene, and (5) sigmatropic rearrangement in toluene at 220-degrees-C to form the fused dienes 1a and 1b. The enantiomeric purities of 1a and 1b were confirmed with the use of a chiral lanthanide H-1 NMR shift reagent. The cyclopentadienes 1 were metalated to form the following complexes: bis-(BCO-Cp)dichlorotitanium, bis(BCO-Cp)dichlorozirconium, and bis(BCO-Cp)chloroxoniobium. All complexes were ientified by their spectral and analytical data. The structure of the enantiomerically pure bis(dimethyl-BCO-Cp)dichlorotitanium complex 14 was determined by X-ray crystallography (two independent molecules in the P2(1) space group, a = 7.216 angstrom, b = 18.621 angstrom, c = 17.557 angstrom, beta = 91.48-degrees, d = 1.31 (calcd, Z = 4) g cm-3). The structure was resolved by direct methods and refined by least squares to R = 4.1% (R(w) = 4.6%).