Formation of Allylpalladium Complexes and Asymmetric Allylation Involving Modular Bridging Diamidophosphite-Sulfides Based on 1,4-Thioether Alcohols

TADDOL-based P,S-bidentate phosphoramidite ligands in palladium-catalyzed asymmetric allylic substitution

A series of easy-to-prepare and modular chiral P,S-bidentate phosphoramidites were synthesized. With respect to Pd(II), these ligands showed the ability to form stable P,S-chelate allylic complexes. The structures of the ligands and their complexes were confirmed by 2D NMR spectroscopy and single-crystal X-ray diffraction. These chiral inducers provided up to 99% ee in the Pd-catalyzed asymmetric allylic substitution of (E)-1,3-diphenylallyl acetate with C- and N-nucleophiles and up to 94% ee in the Pd-mediated allylic alkylation of cinnamyl esters with β-ketoesters and 2,5-dimethylpyrrole. Furthermore, up to 92% ee with quantitative conversion and chemo- and regioselectivity was achieved in the rare reaction between 2-(diethoxyphosphoryl)-1-phenylallyl acetate and aniline. The effects of the structural parameters, reaction conditions and ligand-to-metal ratio on the catalytic results are discussed. It was shown that the ligands surpass their analogues with different denticity.

Evolution of a 'privileged' P-alkene ligand: added planar chirality beats BINOL axial chirality in catalytic asymmetric C-C bond formation

Alkene planar chirality is introduced in the 'privileged' P-alkene phosphoramidite ligand 1. The resulting diastereomeric ligands (pR,R)-5 and (pS,R)-5 form optically pure complexes of Rh(I) and Pd(II), which catalyze conjugate additions of boron C-nucleophiles to enones and allylic alkylations, respectively. In the Rh-catalyzed reaction, the planar chirality of the alkene exerts absolute enantiocontrol over the potent BINOL auxiliary.

Enantioselective [1,2]-Stevens Rearrangement of Thiosulfonates to Construct Dithio-Substituted Quaternary Carbon Centers

An enantioselective [1,2] Stevens rearrangement was realized by using chiral guanidine and copper(i) complexes. Bis-sulfuration of α-diazocarbonyl compounds was developed through using thiosulfonates as the sulfenylating agent. It was undoubtedly an atom-economic process providing an efficient route to access novel chiral dithioketal derivatives, affording the corresponding products in good yields (up to 90% yield) and enantioselectivities (up to 96 : 4 er). A novel catalytic cycle was proposed to rationalize the reaction process and enantiocontrol.

An asymmetric [1,2] Stevens rearrangement was realized via chiral guanidine and copper(i) complexes. A series of novel chiral dithioketal derivatives were obtained with good yields (up to 90% yield) and enantioselectivities (up to 96 : 4 er).