New chiral ferrocenyloxazolines: The first planar chiral triferrocenylmethane derivative and its use in asymmetric catalysis

New planar chiral enantiopure ferrocenyloxazolines have been prepared including ferrocenyldiphenylmethanol, diferrocenylphenylmethanol and triferrocenylmethanol derivatives (S,pR)-10 - (S,pR)-12, the latter being the first chiral triferrocenylmethanol derivative. The ferrocenyldiphenylmethanol derivative (S,pR)-10 has been crystallographically characterized. Asymmetric ethylation of some arylaldehydes using diethylzinc in the presence of the planar chiral triferrocenylmethanol derivative (S,pR)-12 afforded good yields and ees, which were higher than those obtained with related ferrocenyloxazolines.     

New phosphorus dendrimers with chiral ferrocenyl phosphine-thioether ligands on the periphery for asymmetric catalysis

Chiral ferrocenyl phosphine-thioether ligands have been covalently bound on the periphery of 4 phosphorus dendrimers (generations 1-4) having a cyclotriphosphazene core and on one model compound. These new dendrimers proved to be efficient ligands for the palladium-catalyzed asymmetric allylic substitution reaction (ee up to 93%).     

Palladium complexes of phosphinamine ligands in the intramolecular asymmetric Heck reaction

The synthesis of two novel cyclisation substrates for the asymmetric intramolecular Heck reaction is reported. Their cyclisation, in addition to a known substrate for cis-decalin formation, were tested with palladium complexes of BINAP and heterobidentate oxazoline-containing ligands. In general BINAP provides a more active catalyst system for the range of substrates tested although excellent enantioselectivities of up to 85% were obtained with the P,N ligands studied. A trend was noted whereby the t-leucine-derived oxazoline ligands were more reactive and enantioselective than the valine-derived analogues. Similarly, the diphenylphosphinoferrocenyloxazoline ligands were more reactive and selective than the corresponding diphenylphosphinophenyloxazoline ligands.     

New Ligands for Regio- and Enantiocontrol in Pd-Catalyzed Allylic Alkylations

The branched, chiral products 1 are formed preferentially in the allylic alkylations in Equation (1) when the Pd catalyst contains the P,N ligand L* or derivatives thereof. The ligands are readily synthesized from commercially available precursors.     

The use of a new carboranylamidophosphite ligand in the asymmetric Pd-catalysed allylic alkylation in organic solvents and supercritical carbon dioxide

A novel P-monodentate ligand based on carboranyl alcohol and (S)-2-(anilinomethyl)pyrrolidine provides high enantioselectivities (ee’s up to 95%) in the Pd-catalyzed allylic alkylation of (E)-1,3-diphenylallyl acetate. The first example of the Pd-catalysed allylic alkylation in supercritical carbon dioxide is also described.     

New tagged naplephos ligands for asymmetric allylic substitutions under traditional and unconventional conditions

This paper demonstrates the versatility of the class of chiral ligands naplephos, which has been further refined by preparing new ‘tagged’ versions for selective use in polar media (e.g., ionic liquids). These modified types, along with the best performing original varieties, have been examined in two Pd-catalysed asymmetric processes involving C-C and C-N bond formation. High ees have been achieved in traditional solvents, while the experiments performed in ionic liquids confirm the difficulty of predicting the outcome of a reaction in these media and the general decrease in the catalytic performance.     

The first example of atropisomeric amide-derived P,O-ligands used for an asymmetric Heck reaction

Atropisomeric N,N-diisopropyl 2-diphenylphosphino- and 2-di(tert-butyl)phosphino-1-naphthamides were used, for the first time, as bidentate P,O-ligands for intermolecular asymmetric Heck reactions of 2,3-dihydrofuran with aryl triflates. The reactions were carried out in the presence of 4 mol% Pd(OAc)₂, 8 mol% of the axially chiral ligand, and 3 equiv. of (i-Pr)₂NEt in THF at 60 °C for 3 days. Optically active 2-aryl-2,5-dihydrofurans were obtained as the major products along with the rearranged 2-aryl-2,3-dihydrofurans. Enantioselectivity up to 55.2% ee was obtained for the major product.     

Synthesis of chiral 2-alkyl-8-quinolinyl-oxazoline ligands: reversal of enantioselectivity in the asymmetric palladium-catalyzed allylic alkylation

New chiral 2-alkyl-8-quinolinyl-oxazolines were synthesized from 2-alkyl-8-quinolinecarboxylic acids and enantiomerically pure amino alcohols using a convenient procedure. Enantioselective palladium-catalyzed allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate in the presence of 2-alkyl-8-quinolinyl-oxazolines provided an alkylation product with an opposite configuration compared to those obtained from unsubstituted quinolinyl-oxazoline ligands.     

New phosphine-imine and phosphine-amine ligands derived from d-gluco-, d-galacto- and d-allosamine in Pd-catalysed asymmetric allylic alkylation

New phosphine-imine and phosphine-amine chiral ligands which were easily prepared from d-gluco-, d-galacto- and d-allosamine furnished a high level of enantiomeric excess (up to 99%) in the Pd(0)-catalysed asymmetric allylic alkylation of racemic 1,3-diphenyl-2-propenyl acetate with malonates.     

New developments in zinc-catalyzed asymmetric hydrosilylation of ketones with PMHS

The influence of structural modifications of the diamine ligand and the ZnR₂ precursor in the [ZnR₂-diamine]-catalyzed asymmetric hydrosilylation of prochiral ketones with PMHS in aprotic medium is reported. A new diamine ligand giving up to 91% ee in the reduction of acetophenone is described. The scope of this reduction system has been investigated using variously functionalized ketones and some deactivation pathways have been identified.     

Mechanistic Implications of the Observation of Kinetic Resolution in a Palladium-Catalyzed Enantioselective Allylic Alkylation

Preferential rotation in substrate—palladium intermediates in a catalyzed asymmetric allylic alkylation is proposed to be responsible for both the observed kinetic resolution of the racemic allylic acetate starting material as well as the high selectivity found in the enantiodiscriminating product-forming step [Eq. (a)].     

Enantioselective Allylic Substitution of Cyclic Substrates by Catalysis with Palladium Complexes of P,N-Chelate Ligands with a Cymantrene Unit

Mechanistic considerations made a decisive contribution to the development of new chiral P,N ligands L* containing tricarbonylcyclopentadienylmanganese (cymantrene). These ligands induce very high enantioselectivities (>99:1) in allylic substitutions of cyclic substrates 1 with formation of 2 (2-Bp=2-biphenylyl).     

2-Pyridylsulfinamides as effective catalysts in the asymmetric alkylation of aldehydes with diethylzinc

Chiral 2-pyridylsulfinamides were shown to be effective catalysts in the alkylation of aryl and alkyl aldehydes with diethylzinc providing the corresponding alcohols in excellent enantioselectivity. Sulfinamide catalysts possessing solitary chirality at the sulfur center produced the product phenethyl alcohol in good enantioselectivity. Diastereomeric sulfinamides possessing chirality at the carbon-bearing nitrogen and at the sulfur of the sulfinamide increased the enantioselectivity of the product alcohols up to >99%. However, there is no effect of the match-mismatch pair of sulfinamide diastereomers on the outcome of the chiral induction of the product phenethyl alcohols. It was conclusively proved that chirality at the sulfur center is mandatory for obtaining good enantioselectivity in the reaction.     

A P-chiral bisdiamidophosphite ligand with a 1,4:3,6-dianhydro-d-mannite backbone and its application in asymmetric catalysis

A novel readily available P,P-bidentate diamidophosphite ligand with P^∗-stereocentres is prepared from an inexpensive C₂-symmetric 1,4:3,6-dianhydro-d-mannite. By using this efficient ligand, up to 98% ee is achieved in Pd-catalysed asymmetric allylic alkylation, up to 92% ee in Pd-catalysed asymmetric allylic amination and up to 87% ee in Rh-catalysed asymmetric hydrogenation. The influence of the precatalyst, substrate and solvent on the enantioselectivity is discussed.     

Reversal of aryl bromide reactivity in Pd-catalysed aryl amination reactions promoted by a hemilabile aminophosphine ligand

Incorporation of a hemilabile amino group with a bulky, electron-rich phosphorus ligand led to a reversal in the order of aryl bromide reactivity in Pd-catalysed aryl amination reactions.     

Highly substituted furans from 2-propynyl-1,3-dicarbonyls and organic halides or triflates via the oxypalladation-reductive elimination domino reaction

The palladium-catalysed reaction of 2-propynyl-1,3-dicarbonyls with organic halides or triflates provides an efficient straightforward entry into highly substituted furans. The best results have been obtained by using an excess of the alkyne. The process can tolerate a wide variety of important functional groups both on the alkyne and the organic halide or triflate. Under an atmosphere of carbon monoxide, the reaction affords furan derivatives incorporating carbon monoxide. Depending on the alkyne to organic halide or triflate ratio, acyl furans (incorporating one molecule of carbon monoxide) or enol esters (incorporating two molecules of carbon monoxide) can be isolated as the main products.