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Modification of the Atropisomeric N,N-Ligand 2,2'-Di(pyridin-2-yl)-1,1'-binaphthalene and Its Application to the Asymmetric Allylation of Benzaldehyde

2003; Wiley-VCH; Volume: 68; Issue: 5 Linguagem: Inglês

10.1135/cccc20030865

1212-6950

J.P.H. Charmant, N.J. Hunt, Guy C. Lloyd‐Jones, Thorsten Nowak,

Coordination Chemistry and Organometallics

The atropisomeric compound 2,2'-di(pyridin-2-yl)-1,1'-binaphthalene ( 1 ) has been chlorinated, via its bis- N -oxide 2 , at the 4 and 6 pyridine ring positions so as to generate the three isomeric species: 2,2'-bis(6-chloropyridin-2-yl)- ( 3a ), 2-(4-chloropyridin-2-yl)-2'-(6-chloropyridin-2-yl)- ( 3b ) and 2,2'-bis(4-chloropyridin-2-yl)-1,1'-binaphthalene ( 3c ). The dichlorinated compounds underwent Ni-catalysed Kumada cross-coupling with MeMgI to give the methylated pyridine isomers: 2,2'-bis(6-methylpyridin-2-yl)- ( 4a ), 2-(4-methylpyridin-2-yl)-2'-(6-methylpyridin-2-yl)- ( 4b ) and 2,2'-bis(4-methylpyridin-2-yl)-1,1'-binaphthalene ( 4c ). The enantiomerically pure forms of the six novel ligands ( 3a - 3c and 4a - 4c ), prepared from enantiomerically pure 2,2'-di(pyridin-2-yl)-1,1'-binaphthalene ( 1 ), were tested in asymmetric catalysis, but proved to be no better and in most cases poorer than parent 1 . The coordination of the ligands to Zn and Pd fragments has been explored and compared with the parent compound 1 so as to rationalise the negative effect of pyridine substitution on asymmetric induction in the zinc-catalysed allylation of benzaldehyde.