Asymmetric platinum group metal-catalyzed carbonyl-ene reactions: Carbon-carbon bond formation versus isomerization

Academic Article

Abstract

  • A comparative study of the carbonyl-ene reaction between a range of 1,1′-disubstituted or trisubstituted alkenes and ethyl trifluoropyruvate catalyzed by Lewis acid-platinum group metal complexes of the type [M{(R)-BINAP}] 2+ (M = Pt, Pd, Ni; BINAP is 2,2′- bis(diphenylphosphino)-1,1′-binaphthyl) revealed subtle but significant differences in their reactivity. For instance, the palladium-based Lewis acid [Pd{(R)-BINAP}] 2+ catalyzes the ene reaction between methylene cycloalkane to afford the expected α-hydroxy ester in good yield and excellent diastereo- and enantioselectivity. In contrast, under the same conditions, the corresponding [M{(R)-BINAP}] 2+ (M = Pt, Ni) catalyzes isomerization of methylene cycloalkane and the ene reaction of the resulting mixture of methylene cycloalkane and 1-methylcycloalkene at similar rates to afford a range of α-hydroxy esters in high regioselectivity, good diastereoselectivity, and good to excellent enantioselectivity. In addition, [Pt{(R)-BINAP}] 2+ also catalyzes postreaction isomerization of the ene product as well as consecutive ene reactions to afford a double carbonyl-ene product. The sense of asymmetric induction has been established by single-crystal X-ray crystallography, and a stereochemical model consistent with the formation of (S)-configured α-hydroxy ester has been proposed; the same model also accounts for the observed exo-diastereoselectivity as well as the level of diastereoselectivity. © 2006 American Chemical Society.
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    Author List

  • Doherty S; Knight JG; Smyth CH; Harrington RW; Clegg W
  • Start Page

  • 9751
  • End Page

  • 9764
  • Volume

  • 71
  • Issue

  • 26