Pd-catalyzed Allylic Reactions Research Articles

Design of P-Chirogenic Aminophosphine-Phosphinite Ligands at Both Phosphorus Centers: Origin of Enantioselectivities in Pd-Catalyzed Allylic Reactions.

We have recently patented an unprecedented stereospecific N → O phosphinyl migration process which transforms P-chirogenic aminophosphines into phosphinites. A fine design of aminophosphine phosphinite ligands (AMPP*) derived from ephedrine and bearing a P-chirogenic center either at the aminophosphine or phosphinite moiety was performed. The synthesis of AMPP* ligands with a P-chirogenic aminophosphine moiety was based on the well-established stereospecific reaction of oxazaphospholidine borane with organolithium reagents, followed by trapping with a chlorophosphine and borane decomplexation. Concurrently, the preparation of AMPP* ligands with a P-chirogenic phosphinite moiety was performed by N → O phosphinyl migration of aminophosphines borane by heating at 50 °C with DABCO and then reaction with chlorophosphines. AMPP* ligands were studied in palladium-catalyzed asymmetric allylic alkylations, leading to enantioselectivities from 91% (R) to 95% ee (S). X-ray crystallographic data for relevant Pd-AMPP* complexes and computer modeling explained the origin of the enantioselectivities based on MO interactions of most stable conformers with nucleophiles.

Design, Synthesis, and Applications of Potential Substitutes of t-Bu-Phosphinooxazoline in Pd-Catalyzed Asymmetric Transformations and Their Use for the Improvement of the Enantioselectivity in the Pd-Catalyzed Allylation Reaction of Fluorinated Allyl Enol Carbonates

The design, synthesis, and applications of potential substitutes of t-Bu-PHOX in asymmetric catalysis is reported. The design relies on the incorporation of geminal substituents at C5 in combination with a substituent at C4 other than t-butyl (i-Pr, i-Bu, or s-Bu). Most of these new members of the PHOX ligand family behave similarly in terms of stereoinduction to t-Bu-PHOX in three palladium-catalyzed asymmetric transformations. Electronically modified ligands were also prepared and used to improve the enantioselectivity in the Pd-catalyzed allylation reaction of fluorinated allyl enol carbonates.

Mechanical Stirring Speed in Water/Hexane Biphasic Catalyst Controls Regioselectivity of Pd-catalyzed Allylation Reaction

Abstract Vigorous mechanical mixing of the water/hexane biphasic Pd-catalyzed allylation of benzenethiol gave sterically congested allyl sulfides, due to high reactivity of the enforced orientation of the η1-allylpalladium intermediate at the solvent interface.

Unexpected effect of the fluorine atom on the optimal ligand-to-palladium ratio in the enantioselective Pd-catalyzed allylation reaction of fluorinated enol carbonates

The enantioselective Pd-catalyzed allylation reaction of fluorinated allyl enol carbonates is presented; a key feature of this transformation is the important effect of the ligand-to-palladium ratio on the enantioselectivity of the alpha-fluoroketones, since using a ligand excess (L/Pd ratio = 1.25 : 1) led to moderate results (30-76% ee), while using a L/Pd ratio <1 : 1.67 (to as low as 1 : 4) allowed the desired products to be obtained with high enantiopurity (up to 94% ee).

Enantioselective Pd-Catalyzed Allylation Reaction of Fluorinated Silyl Enol Ethers

An enantioselective Pd-catalyzed allylation reaction of fluorinated silyl enol ethers is reported. This reaction provides a stereoselective and efficient approach to allylated tertiary α-fluoroketones from achiral fluorinated precursors. A variety of cyclic silyl enol ether can be used, and the yields of the desired products range from 52 to 93%, and the enantiomeric excesses range from 83 to 95% ee.

Formation of Quaternary Carbon Center with a Trifluoromethyl Group Using a Pd-Catalyzed Allylation Reaction

Synthesis of compounds with quaternary carbons is one of the most attractive reactions in the synthetic chemistry. However, there are only a few reports on synthesis of the compounds with a fluoroalkyl group at a quaternary carbon center. Recently, we reported the synthesis of alpha-trifluoromethylated ketones by the reaction of alpha,beta-unsaturated ketones with CF(3)-I using a Rh catalyst. When the alpha-trifluoromethylated ketones and allyl carbonates were treated with a Pd catalyst, the allylation reaction proceeded smoothly at the trifluoromethylated carbon to give the desired compounds with a trifluoromethylated quaternary carbon center in good to excellent yields.