An alcohol-directed, nickel-catalyzed
three-component umpolung
carboamination of unactivated alkenes with aryl/alkenylboronic esters
and electrophilic aminating reagents is reported. This transformation
is enabled by specifically tailored O-(2,6-dimethoxybenzoyl)hydroxylamine
electrophiles that suppress competitive processes, including undesired
β-hydride elimination and transesterification between the alcohol
substrate and electrophile. The reaction delivers the desired 1,2-carboaminated
products with generally high regio- and syn-diastereoselectivity
and exhibits a broad scope of coupling partners and alkenes, including
complex natural products. Various mechanistic experiments and analysis
of the stereochemical outcome with a cyclic alkene substrate, as confirmed
by X-ray crystallographic analysis, support alcohol-directed syn-insertion of an organonickel(I) species.
Methoxide abstraction from gold acetylide complexes of the form (L)Au[η -C≡CC(OMe)ArAr'] (L=IPr, P( Bu) (ortho-biphenyl); Ar/Ar'=C H X where X=H, Cl, Me, OMe) with trimethylsilyl trifluoromethanesulfonate (TMSOTf) at -78 °C resulted in the formation of the corresponding cationic gold diarylallenylidene complexes [(L)Au=C=C=CArAr'] OTf in ≥85±5 % yield according to H NMR analysis. C NMR and IR spectroscopic analysis of these complexes established the arene-dependent delocalization of positive charge on both the C1 and C3 allenylidene carbon atoms. The diphenylallenylidene complex [(IPr)Au=C=C=CPh ] OTf reacted with heteroatom nucleophiles at the allenylidene C1 and/or C3 carbon atom.
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