Novel Chiral Biferrocene Ligands for Palladium-Catalyzed Allylic Substitution Reactions

Abstract

Eleven novel aminophosphine ligands have been synthesized, all of which contain a chiral 2,2' '-bridged biferroceno unit as part of a biferrocenoazepine substructure. The efficiency of these compounds as chiral auxiliaries in palladium-mediated allylic substitution reactions has been investigated. Depending on the degree of (steric) fit between proper ligands and cyclic or noncyclic substrates, reactions with 46-87% ee were achieved. The molecular structure of a palladium dichloride complex of one of the ligands was determined by X-ray diffraction and compared to its binaphthyl analogue. In the solid state, the azepine substructure of these two complexes adopts totally different conformations with either local C(2) (binaphthyl) or local C(1) (biferrocene derivative) symmetry. These structural changes are well-reproduced by empirical force field calculations and are also reflected in significantly different behavior in asymmetric catalysis.

(−)‐Sparteine‐Mediated Directed ortho‐Metalation of N‐Cumyl‐N‐ethylferrocenecarboxamide. Versatile Routes to Functionalized Planar Chiral Ferrocenecarboxamides, Amines, Esters and Phosphines

“…Standard work-up followed by column chromatography (hexanes:EtOAc, 70:30) afforded 16 as an unstable red-orange oil which darkened quickly in air; yield: 0.542 g (89%). The compound was used immediately for the preparation of 17; IR (NaCl, neat): n max 2979, 2873, 1672, 1635 cm (S)-2-Vinyl-N-cumyl-N-ethylferrocenecarboxamide (17) Crude carbinol pre-17, prepared as described above from aldehyde 16 (449 mg, 1.11 mmol), was dissolved in a roundbottomed flask in THF (12 mL) under argon and the solution was cooled to 0 8C with stirring. NaH (88 mg, 60% dispersion in mineral oil,~2.2 mmol) was added, and the mixture was heated at reflux for 5 h. After cooling to 0 8C, water was added and the product was extracted with Et 2 O followed by CH 2 Cl 2 (Â 2) and the combined organic extract was dried (anhydrous MgSO 4 (S)-2-Vinyl-N-allyl-N-ethylferrocenecarboxamide (18) NaH (92 mg, 60% dispersion in mineral oil,~2.3 mmol) was washed with hexanes (4 mL), and the solvent was carefully removed by syringe and replaced with DMF (3 mL).…”

“…[16] Attempted double Charette esterification of (R,R)-10 gave the structurally interesting and crystallographically verified [11] azepanone-bridged biferrocene 11 [17] (Figure 2), presumably by nucleophilic attack of one secondary amide group onto a monoimminium triflate intermediate. The key secondary iodoferrocenylamide [18] (R)-7f (Scheme 5) also provided, by alkylation, a facile route to new planar chiral tertiary ferrocenecarboxamides which are inaccessible by direct (À)-sparteine-mediated metalation owing to predicted or potential competing deprotonation at alternate sites.…”

Synthesis of Chiral 2‐Phospha[3]ferrocenophanes and their Behaviour as Organocatalysts in [3+2] Cyclization Reactions

“…[23] This synthetic procedure compares favourably with the previously reported method based on the nucleophilic substitution between SMP and (ferrocenylmethyl)-trimethylammonium iodide. [24] A detailed study of the ortho-metallation of (S,S)-11 (step a) was then conducted. The lithiation-bromination reaction shown in Table 1 has been selected as Scheme 2.…”

Bulky Monodentate Phosphoramidites in Palladium‐Catalyzed Allylic Alkylation Reactions: Aspects of Regioselectivity and Enantioselectivity

“…This is caused by the larger trans influence exerted by P relative to N, thereby rendering the carbon atom trans to phosphorus more electrophilic. [14,[19][20][21][22] Other bidentate PÀN ligands, such as planar, chiral ferrocenyl derivatives, have also been successfully employed, with high regio-and stereoselectivities. [23] The number of chiral monodentate ligands that have been studied in palladium-catalysed asymmetric allylic transformations is rather limited.…”