Synthesis and resolution of 2-methyl-Quinazolinap, a new atropisomeric phosphinamine ligand for asymmetric catalysis

Nickel Complexes in C‒P Bond Formation

This review is a comprehensive account of reactions with the participation of nickel complexes that result in the formation of carbon-phosphorus (C‒P) bonds. The catalytic and non-catalytic reactions with the participation of nickel complexes as the catalysts and the reagents are described. The various classes of starting compounds and the products formed are discussed individually. The several putative mechanisms of the nickel catalysed reactions are also included, thereby providing insights into both the synthetic and the mechanistic aspects of this phosphorus chemistry.

Rhodium-catalyzed asymmetric hydroboration of γ,δ-unsaturated amide derivatives: δ-borylated amides

γ,δ-Unsaturated amides in which the alkene moiety bears an aryl or heteroaryl substituent undergo regioselective rhodium-catalyzed δ-borylation by pinacolborane to afford chiral secondary benzylic boronic esters. The results contrast the γ-borylation of γ,δ-unsaturated amides in which the disubstituted alkene moiety bears only alkyl substituents; the reversal in regiochemistry is coupled with a reversal in the sense of π-facial selectivity.

Enantioselective [2+2+2] cycloisomerisation of alkynes in the synthesis of helicenes: The search for effective chiral ligands

The enantioselective [2+2+2] cycloisomerisation of the aromatic triynes under nickel(0) catalysis to afford nonracemic [6]- and [7]helicene derivatives has been systematically studied. A collection of mono- and bidentate phosphines, phosphites, phosphinites and phosphinous amides possessing stereogenic units such as chiral centre, axis or plane (or their combinations) has been tested and axially chiral binaphthyl-derived monodentate MOP-type phosphine ligands were the optimal class of ligands. Nickel complexes of these ligands afforded nonracemic tetrahydro[6]helicene in up to 64% ee in a model reaction.

Synthesis and Application of Quinazoline−Oxazoline-Containing (Quinazox) Ligands

A practical synthesis of potentially tridentate P,N,N-ligands containing two stereogenic elements incorporated into the axially chiral Quinazolinap and centrally chiral 2-oxazoline subunits is reported. The application of these novel hybrid ligands in Pd(0)-catalyzed asymmetric allylic alkylation revealed the matched and mismatched diastereomer, dominant stereogenic element, as well as the effect of the oxazoline R substituent on the level of enantioselectivity (ee's up to 81%). [structure: see text]

Preparation and Resolution of a Modular Class of Axially Chiral Quinazoline-Containing Ligands and Their Application in Asymmetric Rhodium-Catalyzed Olefin Hydroboration

The preparation and resolution of a series of axially chiral quinazoline-containing ligands is described in which the key steps are the metal-catalyzed naphthyl-phosphorus bond formation, the naphthalene-quinazoline Suzuki coupling, and the preparation of the Suzuki electrophilic components from the corresponding imidate and anthranilic acid. Diastereomeric palladacycles derived from the racemic phosphinamines and (+)-di-mu-chlorobis[(R)-dimethyl(1-(1-naphthyl)ethyl)aminato-C2,N]dipalladium(II) were separated by fractional crystallization. The configuration of the resulting diastereomers was determined by X-ray crystallographic analysis. Displacement of the resolving agent by reaction with 1,2-bis(diphenylphosphino)ethane afforded enantiopure ligand in each case. Their rhodium complexes were prepared and applied in the enantioselective hydroboration of a range of vinylarenes. The quinazolinap catalysts were found to be extremely active, giving excellent conversions, good to complete regioselectivities, and the highest enantioselectivities obtained to date for several members of the vinylarene class, including cis-beta-methylstyrene (97%), cis-stilbene (99%), and indene (99.5%).

Palladium catalyzed cross-coupling reactions for phosphorus–carbon bond formation

Underappreciated in the realm of palladium catalyzed cross-coupling chemistry is the formation of phosphorous-carbon bonds. This tutorial review summarises a collection of important contributions in the area, providing a flavour of the many types of phosphorus species that are participants in palladium catalyzed phosphorus-carbon bond formation. Recent developments include the usage of the cross-coupling reaction for preparation of phosphine ligands and the involvement of low molecular weight phosphinic acid derivatives for the synthesis of unsaturated phosphinic and phosphonic acid derivatives. Mechanistic cycles are offered in some instances. Stereochemical issues are addressed where applicable. The literature is covered to mid 2003.

Rapid formation of triarylphosphines by microwave-assisted transition metal-catalyzed C-p cross-coupling reactions

Rapid, direct transition metal-catalyzed C-P(III) cross-coupling reactions were performed by microwave dielectric heating, employing diphenylphosphine and aryl halides/triflates as substrates. Depending on the specific aryl halide/triflate precursor, the highest yields were obtained utilizing heterogeneous or homogeneous Pd or Ni catalysts in DMF or NMP in the presence of KOAc or DABCO as a base. [reaction: see text]