Diastereoselective Coordination of P-Stereogenic Secondary Phosphines in Copper(I) Chiral Bis(phosphine) Complexes: Structure, Dynamics, and Generation of Phosphido Complexes

Copper-Phosphido Catalysis: Enantioselective Addition of Phosphines to Cyclopropenes

We describe a copper catalyst that promotes the addition of phosphines to cyclopropenes at ambient temperature. A range of cyclopropylphosphines bearing different steric and electronic properties can now be accessed in high yields and enantioselectivities. Enrichment of phosphorus stereocenters is also demonstrated via a Dynamic Kinetic Asymmetric Transformation (DyKAT) process. A combined experimental and theoretical mechanistic study supports an elementary step featuring insertion of a CuI -phosphido into a carbon-carbon double bond. Density functional theory calculations reveal migratory insertion as the rate- and stereo-determining step, followed by a syn-protodemetalation.

Copper-Catalyzed Hydroamination: Enantioselective Addition of Pyrazoles to Cyclopropenes

Chiral N-cyclopropyl pyrazoles and structurally related heterocycles are prepared using an earth-abundant copper catalyst under mild reaction conditions with high regio-, diastereo-, and enantiocontrol. The observed N2:N1 regioselectivity favors the more hindered nitrogen of the pyrazole. Experimental and DFT studies support a unique mechanism that features a five-centered aminocupration.

Copper(I)-Catalyzed Asymmetric Alkylation of Unsymmetrical Secondary Phosphines

A copper(I)-catalyzed asymmetric alkylation of HPAr¹Ar² with alkyl halides is uncovered, which provides an array of P-stereogenic phosphines in generally high yield and enantioselectivity. The electrophilic alkyl halides enjoy a broad substrate scope, including allyl bromides, propargyl bromide, benzyl bromides, and alkyl iodides. Moreover, 11 unsymmetrical diarylphosphines (HPAr¹Ar²) serve as competent pronucleophiles. The present methodology is also successfully applied to catalytic asymmetric double and triple alkylation, and the corresponding products were obtained in moderate diastereo- and excellent enantioselectivities. Some ³¹P NMR experiments indicate that bulky HPPhMes exhibits weak competitively coordinating ability to the Cu(I)-bisphosphine complex, and thus the presence of stoichiometric HPAr¹Ar² does not affect the enantioselectivity significantly. Therefore, the high enantioselectivity in this reaction is attributed to the high performance of the unique Cu(I)-(R,R_P)-TANIAPHOS complex in asymmetric induction. Finally, one monophosphine and two bisphosphines prepared by the present reaction are employed as efficient chiral ligands to afford three structurally diversified Cu(I) complexes, which demonstrates the synthetic utility of the present methodology.

Catalytic Asymmetric Synthesis of P-Stereogenic Phosphines: Beyond Precious Metals

Metal-catalyzed asymmetric synthesis of P-stereogenic phosphines is a potentially useful approach to a class of chiral ligands with valuable applications in asymmetric catalysis. We introduced this idea with chiral platinum and palladium catalysts, exploiting rapid pyramidal inversion in diastereomeric metal–phosphido complexes (ML*(PRR′)) to control phosphorus stereochemistry. This Account summarizes our attempts to develop related synthetic methods using earth-abundant metals, especially copper, in which weaker metal–ligand bonds and faster substitution processes were expected to result in more active catalysts. Indeed, precious metals were not required. Without any transition metals at all, we exploited related P-epimerization processes to prepare enantiomerically pure phosphiranes and secondary phosphine oxides (SPOs) from commercially available chiral epoxides.

1 Introduction

2 Copper-Catalyzed Phosphine Alkylation

3 Copper-Catalyzed Tandem Phosphine Alkylation/Arylation

4 Nickel-Catalyzed Phosphine Alkylation

5 Proton-Mediated P-Epimerization in Synthesis of Chiral Phosphiranes

6 Diastereoselective Synthesis of P-Stereogenic Secondary Phosphine Oxides (SPOs) from (+)-Limonene Oxide

7 Conclusions