Designed Ligands as Probes for the Catalytic Binding Mode in Mo‐Catalyzed Asymmetric Allylic Alkylation.

Abstract

diastereoselective syntheses, enantioselective syntheses diastereoselective syntheses, enantioselective syntheses (incl. cis/trans-isomerism) O 0031 -033Designed Ligands as Probes for the Catalytic Binding Mode in Mo-Catalyzed Asymmetric Allylic Alkylation.-In order to understand the extraordinary levels of regio-and enantioselectivity obtained with the catalytic system based on both enantiomeric ligands [(Ia) or (VIIa)] and molybdenum in the title reaction, the reaction of carbonates (II), (VI), and (VIII) with malonate (III) is studied by use of ligands with modified substituents. The results are compared with those obtained with the original ligands (Ia) and (VIIa). Possible binding modes of these ligands to molybdenum during the catalytic cycle are discussed. -(TROST, BARRY M.; DOGRA,

Pd- and Mo-Catalyzed Asymmetric Allylic Alkylation

“…3. 15 Bidentate coordination with the nitrogen of the pyridine is not required. Indeed, the monopyridine L-7 shows even higher branch selectivity than the bis pyridine L-5 .…”

“…15,40 While the Mo precatalysts were typically the (tris-propionitrile)- or cycloheptatriene-molybdenum tricarbonyl (eq 18), on large scale (2 kg) the more conveniently available Mo(CO) 6 proved satisfactory (eq 19) in a…”

Ligand‐Dependent Mechanistic Dichotomy in Iron‐Catalyzed Allylic Substitutions: σ‐Allyl versus π‐Allyl Mechanism

“…Transition-metal catalyzed allylic substitution has evolved as a powerful tool in this field. [1] In the presence of enantiopure transition-metal catalysts based on Pd, [2] Mo, [3] Ir, [4] Ru [5] , or Ni, [6] enantiomerically enriched products are accessible in good yields starting from racemic material, which is a consequence of the fluctuating character of the intermediate p-allyl metal complexes. In the presence of rhodium [7] or iron catalysts [8] however, a slow isomerization of the s-allyl metal species initially formed is observed, and in the subsequent nucleophilic substitution, retention of constitution and configuration of the starting material occurs.…”

Ligandenabhängige mechanistische Dichotomie in Eisen‐katalysierten allylischen Substitutionen: σ‐Allyl‐ kontra π‐Allyl‐Mechanismus

“…Als eine der effizientesten Methoden hierfür gilt die übergangsmetallkatalysierte, allylische Substitution. [1] In Gegenwart enantiomerenreiner Übergangsmetallkatalysatoren auf Basis von Pd, [2] Mo, [3] Ir, [4] Ru [5] oder Ni [6] erhält man wegen des fluktuierenden Charakters der intermediären p-Allyl-Metall-Komplexe ausgehend von racemischen Reaktanten enantiomerenangereicherte Produkte in guten Ausbeuten. Mit Rh- [7] oder Fe-Katalysatoren [8] isomerisieren die primär gebildeten s-AllylMetall-Komplexe hingegen nur langsam, was zur Folge hat, dass die anschließende nucleophile Substitution unter Erhaltung der formalen Konstitution und Konfiguration abläuft.…”