Catalytic Asymmetric Epoxidations with Chiral Iron Porphyrins

Iron porphyrins have been modified to include optically active functionalities at the meso positions. Asymmetric epoxidations of prochiral olefins with these chiral iron porphyrins and iodosyl compounds have been investigated. Thus, 5α,10β,15α,20β-tetrakis(o-(R)-hydratropamidophenyl)porphyrin (H₂T(α,β,α,β-Hyd)PP) and 5α, 10β,15α,20β-tetrakis(o-[(S)-2′-carboxymethyl-1,1 -binaphthyl-2-carboxamido]phenyl)porphynn (H₂T(a,p,a,p-Binap)PP) were synthesized by the condensation of optically active acid chlorides with 5α,10β,5α,20β-tetrakis(o-arninophenyl)porphyrin. Subsequent insertion of iron into H₂T(a,p,a,p-Hyd)PP and H₂T(a,p,a,p-Binap)PP gave FeT(αβαβ-Hyd)PPCl and FeT(a,p,a,p-Binap)PPCl, respectively. Employing FeT(αβ,αβ-Hyd)PPCl and iodosylbenzene, styrene was oxidized to (R)-(+)-styrene oxide in 31% ee. Similarly, FeT(αβ,αβ-Binap)PPCl and iodosylmesitylene gave (/?)-(+)-styrene oxide in 48% ee. Various substituted styrenes and aliphatic olefins were epoxidized with enantiomeric excesses varying between 0% for 1-methylcyclohexene oxide and 51% for p-chlorostyrene oxide.