Ruthenium-Lewis acid catalyzed asymmetric Diels-Alder reactions between dienes and α,β-unsaturated ketones

The complex [Ru(Cp)(R,R-BIPHOP-F)(acetone)] [SbF6,], (R,R)-1a, was used as catalyst for asymmetric Diels-Alder reactions between dienes (cyclopentadiene, methylcyclopentadiene, isoprene, 2,3-dimethylbutadiene) and alpha,beta-unsaturated ketones (methyl vinyl ketone (MVK), ethyl vinyl ketone, divinyl ketone, alpha-bromovinyl methyl ketone and alpha-chlorovinyl methyl ketone). The cycloaddition products were obtained in yields of 50-90% and with enantioselectivities up to 96% ee. Ethyl vinyl ketone, divinyl ketone and the halogenated vinyl ketones worked best and their reactions with acyclic dienes consistently provided products with > 90% ee. alpha-Chlorovinyl methyl ketone performed better than alpha-bromovinyl methyl ketone. The reaction also provided a [4.3.1]bicyclic ring system in 95% ee through an intramolecular cycloaddition reaction. Crystal structure determinations of [Ru(Cp)((S,S)-BIPHOP-F)(mvk)]-[SbF6], (S,S)-1b, and [Ru(Cp)((R,R)-Me4BIPHOP-F)(acrolein)] [SbF6], (R,R)-2b, provided the basis for a rationalization of the asymmetric induction.