Palladacyclic Imidazoline–Naphthalene Complexes: Synthesis and Catalytic Performance in Pd(II)-Catalyzed Enantioselective Reactions of Allylic Trichloroacetimidates

Abstract

A new family of air- and moisture-stable enantiopure C,N-palladacycles (PIN-acac complexes) were prepared in good overall yield in three steps from 2-iodo-1-naphthoic acid and enantiopure β-amino alcohols. Three of these PIN complexes were characterized by single-crystal X-ray analysis. As anticipated, the naphthalene and imidazoline rings of PIN-acac complexes 18a and 18b were canted significantly from planarity and projected the imidazoline substituents R1 and R2 on opposite faces of the palladium square plane. Fifteen PIN complexes were evaluated as catalysts for the rearrangement of prochiral (E)-allylic trichloroacetimidate 19 (eq 2) and the SN2′ allylic substitution of acetic acid with prochiral (Z)-allylic trichloroacetimidate 23. Although these complexes were kinetically poor catalysts for the Overman rearrangement, they were good catalysts for the allylic substitution reaction, providing branched allylic esters in high yield. However, enantioselectivities were low to moderate and significantly less than that realized with palladacyclic complexes of the COP family. Computational studies support an anti-acetoxypalladation/syn-deoxypalladation mechanism analogous to that observed with COP catalysts. The computational study further suggests that optimizing steric influence in the vicinity of the carbon ligand of a chiral C,N-palladacycle, rather than near the nitrogen heterocycle, is the direction to pursue in future development of improved enantioselective catalysts of this motif.

Tuning StackPhim Ligands: Applications in Enantioselective Borylation and Alkynylation

“…2-Iodo-1-naphthoic acid (5) was prepared on 5-8 g scale in three steps starting from 1-cyanonaphthalene following a procedure reported by Overman and co-workers. 36 Spectroscopic data of 5 satisfactorily matched previously reported data. 36 2-Iodo-N-((1R,2R)-2-(((perfluorophenyl)methyl)amino)cyclohexyl)-1-naphthamide (7) 18 Oxalyl chloride (2.0 M in DCM; 6.71 mL, 13.42 mmol, 2 equiv) was added in a dropwise fashion to a solution of 5 (2.0 g, 6.71 mmol, 1 equiv) and DMF (15 L, 3 mol%) in DCM (17 mL).…”

“…2-Iodo-1-naphthoic acid ( 5 ) was prepared on 5–8 g scale in three steps starting from 1-cyanonaphthalene following a procedure reported by Overman and co-workers. 36 Spectroscopic data of 5 satisfactorily matched previously reported data. 36…”

Rational Design of a Robust Fluorescent Probe for the Detection of Endogenous Carbon Monoxide in Living Zebrafish Embryos and Mouse Tissue

“…As mentioned before, to date, the detection of endogenous CO in living animals remains an unmet challenge. The current fluorescent CO probes such as A1‐Pd and A2‐Pd have relatively unstable coordinated structures and a comparatively small flexible ligand ( A1‐Pd , A2‐Pd ), which may lead to high background fluorescence and short emission wavelengths. Thus, we envisioned that it is necessary to design new fluorescent CO probes with advantageous features such as much higher stability and longer emission wavelengths.…”

Recent Advances in Enantioselective Pd-Catalyzed Allylic Substitution: From Design to Applications

“…Subsequently, the same group developed a new type of air- and moisture-stable enantiopure C,N-palladacycles with an imidazoline-naphthalene backbone as catalysts for the same transformation but they provided lower enantioselectivities than palladacycle 8 . 353 Interestingly, computational studies indicated that the alkene π-bond of the allylic imidate substrate is preferentially coordinated cis to the carbon ligand of the palladacycle with attack of an external nucleophile occurring from the least sterically hindered face in this quadrant (for mechanistic details see section 2.4 ). This suggests that introducing substituents in the vicinity of the carbon donor atom could be a good way to improve the ee values.…”