Most chelation-assisted aliphatic C-H activation proceeds through a kinetically favored five-membered cyclometalated intermediate. Here, we report the first site-selective alkenylation of δ-C(sp(3))-H in the presence of more accessible γ-C(sp(3))-H bonds via a kinetically less favored six-membered palladacycle. A wide range of functional groups are tolerated, and the unique protocol can be applied to the synthesis of chiral piperidines. Moreover, mechanistic insights have been conducted to elucidate the origin of the unusual site-selectivity.
Cp*Cobalt(III)-catalyzed enantioselective
C–H amidation
of ferrocenes using monoprotected amino acids (MPAAs) as chiral ligands
was developed. The reaction was performed under mild conditions in
high yields (up to 97%) with moderate enantioselectivity (up to 77.5:22.5
er), providing a promising strategy to create planar chirality via
base-metal-catalyzed enantioselective C–H activation.
A cobalt(III)-catalyzed C-2 selective C-H alkynylation of indoles using hypervalent iodine-alkyne reagents is described. A broad range of synthetically useful functional groups (-F, -Cl, -Br, -CO2Me, -CN) were tolerated, providing an efficient and robust protocol for the synthesis of C-2 alkynylated indoles. The pyrimidyl and silyl protecting groups could be easily removed to give the corresponding 2-ethynyl-1H-indole.
A Pd(II)-catalyzed sulfonylation of unactivated C(sp(3))-H bonds with sodium arylsulfinates using an 8-aminoquinoline auxiliary is described. This reaction demonstrates excellent functional group tolerance with respect to both the caboxamide starting material and the sodium arylsulfinate coupling partner, affording a broad range of aryl alkyl sulfones. Moreover, the late-stage modification of complex molecules was achieved via this sulfonylation protocol.
A general and practical PdII‐catalyzed intermolecular silylation of primary and secondary C−H bonds of α‐amino acids and simple aliphatic acids is reported. This method provides divergent and stereoselective access to a variety of optical pure β‐silyl‐α‐amino acids, which are useful for genetic technologies and proteomics. It can also be readily performed on a gram scale and the auxiliary can be easily removed with retention of configuration. The synthetic importance of this method is further demonstrated by the late‐stage functionalization of biological small molecules, such as (−)‐santonin and β‐cholic acid. Moreover, several key palladacycles were successfully isolated and characterized to elucidate the mechanism of this β−C(sp3)‐H silylation process.
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