ASYMMETRIC-SYNTHESIS AND METALATION OF A BINAPHTHYLCYCLOPENTADIENE, A C2-SYMMETRICAL CHIRAL CYCLOPENTADIENE

The binaphthylcyclopentadiene 5, abbreviated Binap-Cp, is a C2-symmetric annulated cyclopentadiene possessing axial chirality. This diene is efficiently prepared in four steps via (1) the asymmetric coupling of 1-bromo-2-methylnaphthalene (6) with 1-(bromomagnesio)-2-methylnaphthalene (16) in the presence of catalytic amounts of nickel bromide and the chiral phosphine, (R)-1-[(S)-2-(diphenylphosphino)-ferrocenyl]ethyl methyl ether; (2) bromination of enantiomerically enriched 2,2'-dimethyl-1,1'-binaphthalene (17) with N-bromosuccinimide; (3) bisalkylation of cyclopentadiene to form the spiro-annulated binaphthylcyclopentadiene 15; and (4) sigmatropic rearrangement in toluene at 220-degrees-C to yield the fused diene 5. The enantiomeric purity of 5 was confirmed with the use of a chiral lanthanide H-1 NMR shift reagent. The cyclopentadiene 5 was metalated to form the following complexes: the bis(Binap-Cp)dichlorotitanium 19, the bis(Binap-Cp)dichlorozirconium 22, the (Binap-Cp)dicarbonyliodoiron 26, and the (Binap-Cp)dicarbonylmethyliron 27. All complexes were identified by their spectral and physical data. The structure of the bis(Binap-Cp)dichlorotitanium complex 19 was determined by X-ray crystallography (1:1 racemic complex:hexane crystallized in the C2/c space group, a - 29.611 angstrom, b = 10.902 angstrom, c = 15.868 angstrom, beta = 108.41-degrees, d = 1.101 (calcd, Z = 4) g cm-3). The structure was resolved by direct methods and refined by least squares to R = 4.5% (R(w) = 5.7%). The C2-symmetrical nature of the complex was apparent from the 2-fold axis passing through the titanium.