Rh₂(S‐1,2‐NTTL)₄: A Novel Rh₂(S‐PTTL)₄ Analog With Lower Ligand Symmetry for Asymmetric Synthesis of Chiral Cyclopropylphosphonates

Abstract

A new series of dirhodium(II) tetracarboxylate was derived from N-1,2-naphthaloyl-(S)-amino acid ligands. In terms of enantioselectivity, Rh2 (S-1,2-NTTL)4 () derived from N-1,2-naphthaloyl-(S)-tert-leucine, was the best-performing catalyst among the new series in the enantioselective synthesis of cyclopropylphosphonate derivatives (up to >99% enantiomeric excess). A predictive model was proposed to justify the observed high enantiomeric induction exhibited by Rh2 (S-1,2-NTTL)4 with donor-acceptor phosphonate carbenoids.

Chiral Dirhodium(II) Carboxylates: New Insights into the Effect of Ligand Stereo-Purity on Catalyst Structure and Enantioselectivity

“…The green residue was then purified by means of silica gel column chromatography using ethyl acetate: n-hexane as mobile phase. Spectroscopic data of all prepared complexes were consistent with the previously published literature [36,53].…”

“…825 g, 89%). Spectroscopic data were consistent with the previously published literature [36]. Conditions for chiral HPLC trace: Chiralpak ® IB column, 10% 2-propanol in n-hexane (v/v%) with 0.1% TFA, 0.25 mL/min, 254 nm, τ 1 = 22.5 min, τ 2 = 24.5 min.…”

“…Conditions for chiral HPLC trace: Chiralpak ® IB column, 10% 2-propanol in n-hexane (v/v%) with 0.1% TFA, 0.25 mL/min, 254 nm, τ 1 = 22.5 min, τ 2 = 24.5 min. ; mp 248-249 • C. Spectroscopic data were consistent with the previously published literature [36]. Conditions for chiral HPLC trace: Chiralpak ® ID column, 10% 2-propanol in n-hexane (v/v%) with 0.1% TFA, 0.5 mL/min, 254 nm, τ 1 = 52.5 min, τ 2 = 51.0 min.…”

“…Out of the large dirhodium(II) catalyst family and by following different approaches for catalyst design, several highly enantioselective dirhodium(II) carboxylate catalysts have been reported to date [13,[35][36][37][38][39][40][41][42][43][44]. Our research group, for example, has recently reported a novel approach for the design of dirhodium(II) tetracarboxylate complexes derived from S-amino acid ligands [35,36,45].…”

“…Our research group, for example, has recently reported a novel approach for the design of dirhodium(II) tetracarboxylate complexes derived from S-amino acid ligands [35,36,45]. This approach is founded on tailoring the steric influences of the overall catalyst structure through reducing the local symmetry of the ligand's N-heterocyclic tether.…”