M.C. White, Chem 153 JE-Allyl chemistry -344 Week of December 2. 2002 Allylic substitutions via metal -allyl intermediates Highly regio-and stereoselective allylic substitutions are possible with metal mediated reactions LMcat X=OAc(most common Pd(most common) OCO,Me Moo wo FeO Nio halide, epoxide, sulfone I rh Nu= soft carbanions(malonate) roatom nucleophiles O, N organometallics(main group M" LUMO of allyl cation MIXL ML L HOMO of neutral ligand allyl cation ne representation of a metal T-allyl has the metal in its reduced form and the allyl ligand with a full positive charge ML Mo+2L NuMa+L Consideration of the LUMO of an allyl cation indicates that nucleophilic attack is most likely at the terminal positions of the allyl groupM.C. White, Chem 153 π-Allyl chemistry -344- Week of December 2, 2002 X X = OAc (most common) OCO2Me halide, epoxide, sulfone MnLm cat M = Pd0 (most common) Mo0, W0, Fe0, Ni0, IrI, RhI Nu Nu = soft carbanions (malonate) heteroatom nucleophiles O, N organometallics (main group) Nu Highly regio- and stereoselective allylic substitutions are possible with metal mediated reactions Allylic substitutions via metal π-allyl intermediates General mechanism: MnLm X Mn+2Lm X MnLm One representation of a metal π-allyl has the metal in its reduced form and the allyl ligand with a full positive charge. Consideration of the LUMO of an allyl cation indicates that nucleophilic attack is most likely at the terminal positions of the allyl group. HOMO of allyl cation LUMO of allyl cation Nu or Mn+2Lm X Nu MnLm Nu Nu Mn+2(X)Lm OA L neutral ligand Nu