Synthesis and application of new iminopyridine ligands in the enantioselective palladium-catalyzed allylic alkylation

Abstract

a b s t r a c tA variety of iminopyridines were obtained by condensation of chiral amines with pyridine-2-carboxaldehyde and quinoline-8-carbaldehyde, or of aminoalkylpyridine derivatives with chiral ketones. These ligands were assessed in the enantioselective palladium catalyzed allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate affording the product dimethyl 1,3-diphenylprop-2-enylmalonate in good yields and moderate enantioselectivities (up to 62% ee). Catalytic activity and enantioselectivity were found to be highly dependent upon the steric properties of the ligands. The best enantioselectivity (62% ee) was obtained by an iminopyridine based on a camphane skeleton.

Cu–iminopyridine complexes as catalysts for carbene and nitrene transfer reactions

“…[13] Cu-iminopyridine catalysts were employed either as pre-formed complexes with copper(I) or as in situ formed complexes obtained by adding the ligand to a convenient copper source. The investigated complexes, reported in Scheme 2, were synthesized following literature procedures for related compounds.…”

“…With complex [Cu(L1) 2 ]PF 6 , experiments were performed in order to reduce the large excess of styrene (entries [13][14][15]. Such a change in the reaction conditions, however, led invariably to a concomitant decrease in yield.…”

“…A solution of iminopyridine (1.0 mmol) in dry CH 2 Cl 2 (5 mL) was subsequently injected into the reaction mixture and stirring was continued for an additional 2 h. The solvent was evaporated and the obtained reddish-orange solid was washed three times with dry diethyl ether and dried under reduced pressure. It is worth remarking that in the 1 H and 31 P NMR spectra of the complexes most of the signals of the iminopyridine ligands appear broadened, and in the 13 C NMR spectrum many of them are not even detectable, leaving only the signals of the triphenylphosphine ligand clearly visible. This might be the consequence of dissociation equilibria taking place in solution.…”

Screening of N,N‐bidentate and N,N,N‐tridentate pyridine‐based ligands in the catalytic allylic oxidation of cyclic olefins

“…Iminopyridines 7a , 7b , 7c , 7d , 7e (Fig. ) were formed in one step by reaction of quinoline‐8‐carbaldehyde with chiral amines in diethyl ether containing anhydrous K 2 CO 3 at room temperature . Iminopyridines 8a , 8b , 8c , 8d (Fig.…”

“…1 H NMR and 13 C NMR spectra were recorded using a Varian Mercury ( 1 H, 400.1 MHz; 13 C, 100.6 MHz) with tetramethylsilane as reference. Ligands 4 , 5 , 6a , 6b , 6c , 6d , 7a , 7b , 7c , 7d , 7e , 8a , 8b , 8c , 8d and 8f were prepared according to reported procedures.…”