Calcium catalyzed enantioselective intramolecular alkene hydroamination with chiralC2-symmetric bis-amide ligands

Stegner P, Eyselein J, Ballmann G, Langer J, Schmidt J, Harder S (2021)

Publication Type: Journal article

Publication year: 2021

Journal

Dalton Transactions Royal Society of Chemistry

Book Volume: 50

Pages Range: 3178-3185

Journal Issue: 9

DOI: 10.1039/d1dt00173f

Abstract

The chiral building block (R)-(+)-2,2′-diamino-1,1′-binaphthyl, (R)-BINAM, which is often used as backbone in privileged enantioselective catalysts, was converted to a series ofN-substituted proligandsR1-H2(R = CH2tBu, C(H)Ph2, PPh2, dibenzosuberane, 8-quinoline). After double deprotonation with strong Mg or Ca bases, a series of alkaline earth (Ae) metal catalystsR1-Ae·(THF)nwas obtained. Crystal structures of theseC2-symmetric catalysts have been analyzed by quadrant models which show that the ligands with C(H)Ph2, dibenzosuberane and 8-quinoline substituents should give the best steric discrimination for the enantioselective intramolecular alkene hydroamination (IAH) of the aminoalkenes H2C=CHCH2CR′2CH2NH2(CR′2= CPh2, CCy or CMe2). The dianionicR12−ligand inR1-Ae·(THF)nfunctions as reagent that deprotonates the aminoalkene substrate, while the monoanionic (R1-H)−ligand formed in this reaction functions as a chiral spectator ligand that controls the enantioselectivity of the ring closure reaction. Depending on the substituent R in the BINAM ligand, full cyclization of aminoalkenes to chiral pyrrolidine products as fast as 5 minutes was observed. Product analysis furnished enantioselectivities up to 57% ee, which marks the highest enantioselectivity reported for Ca catalyzed IAH. Higher selectivities are impeded by double protonation of theR12−ligand leading to complete loss of chiral information in the catalytically active species.

Authors with CRIS profile

Philipp Stegner Lehrstuhl für Anorganische und Metallorganische Chemie Jonathan Mai Lehrstuhl für Anorganische und Metallorganische Chemie Gerd Ballmann Lehrstuhl für Anorganische und Metallorganische Chemie Jens Langer Lehrstuhl für Anorganische und Metallorganische Chemie Jochen Schmidt Lehrstuhl für Anorganische und Metallorganische Chemie Sjoerd Harder Lehrstuhl für Anorganische und Metallorganische Chemie

How to cite

APA:

Stegner, P., Eyselein, J., Ballmann, G., Langer, J., Schmidt, J., & Harder, S. (2021). Calcium catalyzed enantioselective intramolecular alkene hydroamination with chiralC2-symmetric bis-amide ligands. Dalton Transactions, 50(9), 3178-3185. https://doi.org/10.1039/d1dt00173f

MLA:

Stegner, Philipp, et al. "Calcium catalyzed enantioselective intramolecular alkene hydroamination with chiralC2-symmetric bis-amide ligands." Dalton Transactions 50.9 (2021): 3178-3185.

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