Synthesis of metal complexes of peptide–phosphinites: Metal complexes in asymmetric Heck reaction

Abstract

The synthesis of seven peptide-derived phosphinites, N-Boc-Phe-Tyr(OPPh 2)-OMe ( 4), N-Boc-Phe-Tyr(OPEt 2)-OMe ( 5), N-Boc-Phe-Tyr(OPCy 2)-OMe ( 6), N-Boc-Phe-Ser(OPPh 2)-OMe ( 7), N-Boc-Phe-Ser(OP t Bu 2)-OMe ( 8), N-Boc-Phe-Thr(OPPh 2)-OMe ( 9), N-Boc-Phe-Thr(OP tBu 2)-OMe ( 10) is reported. These ligands are readily coordinated to Pd(II) and Pt(II) centers giving the corresponding complexes of the type ML 2Cl 2 ( 11– 20). The palladium complexes, [ N-Boc-Phe-Tyr(OPPh 2)-OMe] 2PdCl 2 ( 16), [ N-Boc-Phe-Tyr(OPEt 2)-OMe] 2PdCl 2 ( 17), [ N-Boc-Phe-Tyr(OPCy 2)-OMe] 2PdCl 2 ( 18), [ N-Boc-Phe-Ser(OPPh 2)-OMe] 2PdCl 2 ( 19) and [ N-Boc-Phe-Thr(OPPh 2)-OMe] 2PdCl 2 ( 20) catalyze the asymmetric phenylation of 2,3-dihydrofuran in moderate to high yields with high ee’s. The steric and electronic influences of the ligand substituents in driving the catalytic process are also discussed.