Ferrocene-based planar chiral imidazopyridinium salts for catalysis.

Planar chirality remains an underutilized control element in asymmetric catalysis. Factors that have limited its broader application in catalysis include poor catalyst performance and difficulties associated with the economical production of enantiopure planar chiral compounds. The construction of planar chiral azolium salts that incorporate a sterically demanding iron sandwich complex is now reported. Applications of this new N-heterocyclic carbene as both an organocatalyst and a ligand for transition-metal catalysis demonstrate its unprecedented versatility and potential broad utility in asymmetric catalysis.

N-heterocyclic-carbene-catalyzed synthesis of 2-aryl indoles.

A convergent and efficient transition-metal-free catalytic synthesis of 2-aryl-indoles has been developed. The interception of a highly reactive and transient aza-ortho-quinone methide by an acyl anion equivalent generated through N-hetereocyclic carbene catalysis is central to this successful strategy. High yields and a wide scope as well as the streamlined synthesis of a kinase inhibitor are reported.

A survey of sulfide ligands for allylic C-H oxidations of terminal olefins.

Perfect to a THT! Screening a diverse library of thioether ligands led to the discovery of tetrahydrothiophene (THT) as a highly reactive and selective ligand for Pd-catalyzed allylic CH oxidation reactions. This novel ligand system provides some of the highest reported yields for the formation of (E)-linear allylic acetates through allylic CH activation chemistry (BQ = 1,4-benzoquinone).

Oxidant-controlled stereoselectivity in the Pd-catalyzed allylic oxidation of cis-vinylsilanes.

The allylic oxidation of cis-vinylsilanes is reported. The reaction requires a low catalyst loading of Pd(OAc)(2) without the need for an external ligand. Interestingly, trans-vinylsilanes are unreactive, whereas allylic oxidations of cis-vinylsilanes proceed in good yields giving a single diastereo- and regioisomer of the branched allylic acetate trans-vinylsilane when benzoquinone is employed. The use of PhI(OAc)(2) as oxidant in place of benzoquinone provides the branched, cis-vinylsilane as the major product. Additionally, the first intramolecular allylic C-H etherifications of cis-vinylsilanes to give oxygen heterocycles are also described.

Allylic oxidations of terminal olefins using a palladium thioether catalyst.

A palladium catalyst that converts terminal olefins to linear allylic acetates at lower catalyst loadings and faster reaction times than current systems is reported. This reaction can be conducted using benzoquinone as the oxidizing agent or catalytic amounts of copper and hydroquinone under one atmosphere of oxygen. Preliminary reactivity studies of pi-allylpalladium complexes under our reaction conditions do not provide results similar to those obtained in the catalytic reaction, which may suggest an alternative reaction pathway. The palladium catalyst is ligated by an aryloxyalkyl aryl sulfide, which is identified as a new ligand for homogeneous catalysis.