Synthesis of Versatile Chiral N,P Ligands Derived from Pyridine and Quinoline

Abstract

Chiral phosphanyl oxazolines 1 (PHOX) [1] and related compounds such as 2[2] and 3 [3] have established themselves as highly versatile, readily accessible ligands for controlling the stereochemistry of metal-catalyzed reactions. The success of these ligands in the Ir-catalyzed hydrogenation of olefins [2][3][4] and imines, [5] and the intention to mimic the coordination sphere of Crabtree's catalyst ([(Cy 3 P)(pyridine)Ir(cod)]PF 6 ) [6] (Cy = cyclohexyl, cod = 1,5-cyclooctadiene) with a chiral bidentate ligand, motivated us to prepare chiral pyridyl phosphanes having the general structure 4.[7] On the basis of simple force-field calculations carried out with a fixed standard geometry for the P-Ir-N core and the known propensity of 2-(oxymethyl)pyridines to adopt an antiperiplanar conformation of the N-C-C-O fragment, [8] we anticipated that these ligands would form a rigid chelate ring in a[*] Dr.

BINAP versus BINAP(O) in Asymmetric Intermolecular Mizoroki–Heck Reactions: Substantial Effects on Selectivities

“…With iPr 2 NEt as the base (Table 1, entries 1 and 4), the arylation was perfectly regiodivergent for BINAP(O) (1!2) and BINAP (1!3). The preference for formation of 2 versus 3 resembles that of P,N ligands; [9,11] hemilabile BINAP(O) is also a ligand with a stronger and weaker donor atom (PPh 2 and P(O)Ph 2 ). [16] A similar result had been obtained with 2-diphenylarsino-2'-diphenylphosphino-1,1'-binaphthyl (BINAPAs), a BINAP analogue with a PPh 2 group and a poorly donating AsPh 2 group (2/3 = 62:38).…”

“…Conversely, predominant formation of 2 (no migration) is observed with bidentate P,N ligands, [9][10][11] often combined with [Pd 2 -A C H T U N G T R E N N U N G (dba) 3 ]·dba or [PdA C H T U N G T R E N N U N G (dba) 2 ] (dba= dibenzylideneacetone). These well-documented experimental observations [3] are in full accordance with a statement by Hii et al, [5] who reported that release of the alkene from an intermediate alkenepalladium(II) hydride complex is faster with P,N (no migration) than with P,P (migration) chelating ligands.…”

Enantioselective Reduction of Diaryl Ketones Catalyzed by a Carbonyl Reductase from Sporobolomyces salmonicolor and its Mutant Enzymes

“…The organic extract was dried over anhydrous sodium sulfate and subjected to chiral HPLC analysis to determine the conversion and enantiomeric excess. The absolute configurations of product alcohols were identified by comparing the HPLC elution sequence with the literature data using the same type of column, [6,7,17,[40][41][42][43][44] and/or by comparing with the enantiomerically enriched sample prepared by literature methods. [30] General Procedure for Enzymatic Reduction of 4-Methylbenzophenone and 4-Methoxybenzophenone (Preparative Scale)…”

Iridium Catalysts with Bicyclic Pyridine–Phosphinite Ligands: Asymmetric Hydrogenation of Olefins and Furan Derivatives

“…With the intention of mimicking the coordination sphere of the Crabtree catalysts more closely, we also examined a series of pyridine-and quinoline-derived ligands 4 and 5. [8] As the results were quite encouraging, we decided to extend our studies to bicyclic analogues of type 6 because we thought that the more rigid conformation imposed by the additional ring could result in even higher enantioselectivities. Here we report the syntheses of a series of pyridyl-phosphinites 6 and their evaluation as ligands for Ir-catalyzed asymmetric hydrogenation.…”