[reaction: see text] A copper-mediated deracemization of the vaulted biaryl ligands VANOL and VAPOL can be readily achieved in the presence of (-)-spartiene. The optimal procedure involves the in situ generation of copper(II) and leads to the reproducible formation of (S)-VANOL and (S)-VAPOL in greater than 99% ee from the racemates. This method is superior to existing procedures for BINOL (92% ee).

Several derivatives of the vaulted biaryl ligand VAPOL were prepared and evaluated as chiral ligands for aluminum Lewis acids in the catalytic asymmetric Diels–Alder reactions of methyl acrylate and methacrolein with cyclopentadiene. The substituents on VAPOL were introduced into the 6- and 6′-positions in an effort to further extend the chiral pocket of the major groove, which contains the phenol functions at the 4- and 4′-positions. The set of four new ligands that have been prepared have the following groups introduced into the 6- and 6′-positions of VAPOL: bromide, methyl, phenyl and 3,5-di-t-butylphenyl. All of these ligands give lower asymmetric inductions than the unsubstituted VAPOL for the Diels–Alder reactions of both methyl acrylate and methacrolein. The positive cooperativity of added carbonyl compounds on the autoinduction in the Diels–Alder reaction of methyl acrylate and cyclopentadiene were also investigated with the VANOL and VAPOL ligands as well as the 6,6′-dibromo and 6,6′-diphenyl derivatives of VAPOL. Only the reaction with VAPOL showed any significant positive cooperativity. The reaction with VANOL was sluggish at –78 °C, but at higher temperatures, the reaction did exhibit positive cooperativity that was similar to that of VAPOL. Finally, no positive cooperativity was observed with the VAPOL ligand for the reaction of methacrolein and cyclopentadiene.Key words: Diels–Alder, asymmetric catalysis, vaulted biaryl ligands, VANOL, VAPOL.

Other naphthalene derivativesOther naphthalene derivatives Q 1020Highly Enantioselective Deracemization of Linear and Vaulted Biaryl Ligands.-A first copper-mediated deracemization of biaryl ligands VANOL (Ia) and VAPOL (Ib) in the presence of (-)-sparteine is described. The procedure includes the in situ generation of copper(II) and leads to the reproducible formation of the (S)-enantiomers in greater than 99% e.e. from the racemates. -(ZHANG, Y.; YEUNG, S.-M.; WU, H.; HELLER, D. P.; WU, C.; WULFF*, W. D.; Org. Lett. 5 (2003) 11, 1813-1816; Dep. Chem., Mich. State Univ., East Lansing, MI 48824, USA; Eng.) -Steudel 38-074

The new VAPOL derivatives (Ia)-(Id) are prepared and evaluated as chiral ligands for aluminum Lewis acids in the asymmetric Diels-Alder reactions of cyclopentadiene with methacrolein or methyl acrylate. They give significantly lower asymmetric inductions than the previously investigated unsubstituted VAPOL ligand (Ie). -(HELLER, D. P.; GOLDBERG, D. R.; WU, H.; WULFF*, W. D.; Can.