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Asymmetric Pt(II)-catalyzed ene reactions: counterion-dependent additive and diphosphine electronic effects
J H Koh1, A O Larsen, M R Gagné
1Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, USA.
Organic Letters
|May 12, 2001
Abstract:
[reaction: see text]. Catalysis of the glyoxylate-ene reaction by dicationic P2Pt(II) complexes is subject to anion-dependent additive effects. For [((S)-MeOBiphep)Pt](OTf)2 catalysts, acidic phenols such as 3-CF3-C6H3OH or C6F5OH provide substantial rate increases but do not affect the more active SbF6-based catalysts. Enantioselectivity and reactivity also increased with diphosphine basicity, with 4-t-Bu-substituted MeOBiphep ligands yielding the highest enantioselectivities.