New Phosphine Ligand Architectures Lead to Efficient Gold Catalysts for Cycloisomerization Reactions at Very Low Loading
Abstrakt
A simple and efficient access to a new P-chiral, but so far racemic ligand class featuring ortho-trityl and ortho-biaryl motifs is reported. The phosphines are prepared by efficient three- to four-step modular syntheses from simple branched alkyl(diphenyl)phosphine oxides in 52-63% overall yield.
They form stable gold complexes, which were characterized by X-ray crystallography and spectroscopic methods. Fundamental catalytic properties of the complexes were studied in 1,6-enyne cycloisomerization reactions of achiral substrates to benchmark their activity against the efficient achiral catalyst (JohnPhos)AuCl.
The results show that the new complexes can be applied in amounts down to 100 ppm allowing the cycloisomerization reactions to be performed with turnover frequencies of 20000 h(-1) and turnover numbers of up to 10000 h(-1).