[reaction: see text] BINOL-based diphosphonites having achiral backbones are useful ligands in the Rh-catalyzed conjugate addition of arylboronic acids to alpha,beta-unsaturated carbonyl compounds. The nature of the achiral backbone determines the direction and degree of enantioselectivity, with er values of up to 99.5:0.5 possible.

The stereoselective synthesis of P-chirogenic chlorophosphine boranes 4 was investigated by HCl acidolysis of the corresponding aminophosphine boranes 10. The reaction afforded the P-N bond cleavage with inversion of the configuration at the phosphorus center, leading to the chlorophosphine boranes 4 with high to excellent enantiomeric purities (80-99% ee), except in the case of the chloro-1-naphthylphenylphosphine borane 4d. Reaction conditions and workup significantly influence the enantiomeric purity of the product, with the exception of the o-anisyl- and o-tolylchlorophenylphosphine boranes, 4b and 4c, which were found to be particularly stable even after purification by chromatography on silica gel. Reaction of the chlorophosphine boranes 4 with various nucleophiles, such as carbanions, phenolates, thiophenolates, or amides, afforded the corresponding organophosphorus borane complexes via P-C, P-O, P-S, and P-N bond formation, respectively, in 34-93% yield and with up to 99% ee. This work demonstrates the importance of chlorophosphine boranes 4 as new and powerful electrophilic building blocks for the highly stereoselective synthesis of P-chirogenic organophosphorus compounds.

No abstract

An original series of P-chirogenic aminophosphane-phosphinite (AMPP) ligands has been synthesized from (+)-or (-)-ephedrine in 23 to 61 % overall yields by a versatile threestep methodology. The AMPP ligands, bearing either one or two P-chirogenic centers, were used in the form of rhodium complexes for the catalyzed hydrogenation of α-acetamidocinnamate as a test reaction. Notably, even with AMPP ligands all derived from (+)-ephedrine, variation of the substituent on a P-center allowed the phenylalanine derivatives to be obtained in either (S) or (R) absolute configurations, with ee values ranging from 99 % (S) to 88% (R). The asymmetric induction was analyzed with the aid of X-ray structures of AMPP complexes, and a new model for the enantioselectivity, taking into consideration the boat conformation and the steric and electronic dissymmetries at the dihydride