Cyclomagnesiation of Dienes Catalyzed by a Chiral ansa-Zirconocene

SANDRA E. MARTÍN; HANS-HERBERT BRINTZINGER

INORGANICA CHIMICA ACTA

ELSEVIER SCIENCE SA

Lugar: Amsterdam; Año: 1998 vol. 280 p. 189 - 192

0020-1693

The biphenyl-bridged, chiral zirconocene complex rac-2,2´-biphenyl-bis(3,4-dimethyl-cyclopentadienyl)zirconium dichloride catalyzes the reaction of 1,6- and 1,7-dienes with excess dibutyl magnesium to bis(butyl-magnesium-methyl)-substituted cycloalkane derivatives. Analogous reactions occur with butyl magnesium chloride and with heteroatom-containing dienes. The preference of 1,6-dienes for trans-fused cycli­za­tion products and that of 1,7-dienes for cis-fusion at ambient and for trans-fusion at elevated temperatures is similar to that observed before for unsubstituted zirconocene complexes. The R-enantiomer of the biphenyl-bridged zirconocene complex gives trans-fused cyclisation products with an optical purity of only 15% ee. The stereochemistry of these cyclomagnesiation reactions is explained in terms of the relative rates of mutually competing cyclization and transmetalation steps.