Explanation of Different Regioselectivities in the ortho‐Lithiation of Ferrocenyl(phenyl)methanamines

Abstract

Diastereoselective ortho‐lithiation of ferrocenes is a principal strategy for the synthesis of chiral ferrocene ligands. Dilithiation of (R)‐1‐(2‐bromophenyl)‐1‐ferrocenyl‐N,N‐dimethylmethanamine leads to a dilithium intermediate, which can be transformed to a Taniaphos ligand with (R,Rp)‐configuration. On the other hand, lithiation of (R)‐1‐phenyl‐1‐ferrocenyl‐N,N‐dimethylmethanamine affords a lithiated product with opposite configuration of the stereogenic plane. Presumably, the second lithium atom attached at the ortho‐position of the phenyl ring is responsible for this difference through the intramolecular multicenter arrangement involving both lithium atoms and their adjacent carbon atoms, the iron atom of the ferrocenyl moiety, and the nitrogen atom of the amino group. This hypothesis has been supported also by quantum chemical calculations.

Retro‐Brook Rearrangement of Ferrocene‐Derived Silyl Ethers

“…In the C ‐lithiated isomer syn ‐ 13 a positive overlap is observed between the lithium atom and the nearest carbon atoms C1 and C17 of both cyclopentadienyl rings and the Fe atom. A similar Li–Fe interaction was computationally predicted in other derivatives too 28. The shift of the Li atom to an oxygen atom results in shortening of the LiFe distance and thus the overlap of both atoms and the stabilizing interaction increases.…”

Fe–Li Interactions in Ferrocenyllithium Compounds

“…The configuration of the resulting diphosphine contradicts the stereochemistry predicted by the classical model of ferrocenylethanamine ortho ‐lithiation . We have shown that it proceeds via a dilithiated ferrocenyl(phenyl)methanamine intermediate, which is stabilized through the formation of an intramolecular C 2 Li 2 arrangement and possibly also by an intramolecular Fe–Li bond . Recently, we have studied the retro‐Brook rearrangements of (ferrocenylalkyloxy)silanes .…”

Synthesis and Suzuki–Miyaura Cross‐Coupling of Enantioenriched Secondary Potassium β‐Trifluoroboratoamides: Catalytic, Asymmetric Conjugate Addition of Bisboronic Acid and Tetrakis(dimethylamino)diboron to α,β‐Unsaturated Carbonyl Compounds

“…As shown in Figure 2, out of the 50 ligands tested in the reaction, the three ligands providing the highest enantiomeric excess were ROPhos, [19] Tania-phos T001, [20] and (2 R ,5 R )-1-{[(2 R ,5 R )-2,5-diphenylpyrrolidin-1-yl]methylene}-2,5-diphenylpyrrolidinium tetrafluoroborate ( L2 ) [21] (Figure 3). With BBA as the borylating agent, ( R,S )-Josiphos, which proved successful for the addition of B 2 pin 2 , was not effective in the borylation of α , β -unsaturated amides, and led to a trifluoroboratoamide with modest yield and enantiomeric ratio.…”