Formation of Diastereoisomerically Pure Oxazaphospholes and Their Reaction to Chiral Phosphane-Borane Adducts

Abstract

Starting with achiral phosphines and (1S,2S)‐2‐(methylamino)‐1‐phenylpropan‐1‐ol ((+)‐pseudoephedrine) or (1R,2S)‐2‐(methylamino)‐1‐phenylpropan‐1‐ol ((−)‐ephedrine), as chiral auxiliaries, diastereoisomerically pure oxazaphospholes were prepared (Scheme 1). The configuration at the P‐atom is controlled by the configuration at the Ph‐substituted C(1) of (+)‐pseudoephedrine or (−)‐ephedrine, respectively. This was confirmed by X‐ray crystal‐structure analyses of two intermediate compounds in the synthesis route to the chiral triarylborane‐phosphane adducts.

Stereoselective Synthesis of All Possible Phosferrox Ligand Diastereoisomers Displaying Three Elements of Chirality: Stereochemical Optimization for Asymmetric Catalysis

“…Although many methods are known for the stereocontrolled synthesis of P -stereogenic compounds, in this instance efficiency would result if the lithiated planar chiral precursor to phosphorus introduction could be used to control diastereoselectivity. There are several reports in the literature of the reaction of chiral nucleophiles with RPX 2 (X = Cl, NEt 2 ) where differential replacement of both leaving groups X leads to a product in high diastereoselectivity . A further example is the use of lithiated planar chiral Ugi’s amine as the nucleophile for the first step, followed by addition of an aryl Grignard reagent, to give P -stereogenic P–N ligands in high dr …”

“…First, aryl/lone-pair differentiation, with the aryl group oriented away from ferrocene in this cyclic structure, provides a basis for epimerization selectivity. Thermodynamic control of this sort has been used to explain the diastereoselective formation of other auxiliary mediated P -stereogenic derivatives. , Second, stereospecific S N 2 reaction with PhMgBr accounts for the configuration of the phosphorus-based stereogenic center in ( S , S p , R phos )- L4a . Finally, the observed 31 P NMR chemical shift of 67.7 ppm is in reasonable agreement with the value estimated for this intermediate (ca.…”

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

“…The o -anisyl-, α-naphthyl-, , β-naphthyl-, , o -tolyl-, , p -tolyl-, o -biphenyl-, ,, ferrocenyl-, ,, tert -butyl-, , methyl-, , cyclohexyl-, o -[(2-methoxyethoxy)­methoxy]­phenyl-, o -isopropoxyphenyl-, 3,5-xylyl-, 3,5-di- tert -butylphenyl-, 2-(2′,6′-dimethoxy)­biphenyl-, calix[4]­arenyl-, aminophosphines 11a – h , 11j – m , 11o , 11p , and 11u , respectively, were prepared from the appropriate oxazaphospholidine–borane complex (+)- or (−)- 10a or (−)- 10b , according to the described procedure. These compounds exhibited satisfactory analytical and spectrochemical data in agreement with the literature.…”

“…This compound was synthesized from ( S p )-(+)- N -[(1 R ,2 S )-2-hydroxy-1-methyl-2-phenylethyl], N -methylamino­( tert -butyl)­phenylphosphine–borane 11h previously prepared from (+)-ephedrine 9 . , X-ray quality crystals were grown by slow evaporation of hexane. The structure and the data are reported in the SI.…”

Cyclic tri- and Pentavalent Amidoesters and Diamides with a Stereogenic Phosphorus Atom in Asymmetric Synthesis: Part I: Stoichiometric Reagents

“…Reaction of the chlorophosphine boranes 24 with various nucleophiles, such as carbanions, phenolates, thiophenolates, or amides, afforded the corresponding organophosphorus borane complexes 25 via P-C, P-O, P-S, and P-N bond formation, respectively, in 34-93% yield and with up to 99% ee (Scheme 8) [31]. Soon after publication of the first report, this methodology was adopted worldwide [32][33][34][35][36][37][38][39] and very recently several 2,6-disubstituted aryl groups were successfully appended to the phosphorus atom, giving the corresponding, sterically congested (N-ephedrino)phosphine boranes 20a with dr 99:1 [40].…”