Stereocontrol in Preparation of Cyclopalladated Alkylaromatic Oximes and Evaluation of Their Stereoselective Esterase-Type Catalytic Activity

Abstract

The stereochemistry of 2′-methylbutyrophenone oxime, the rates of ortho-palladation of its E-and Zisomers, and catalytic activity of the respective Pd complexes were studied. The full stereoisomeric composition of oximes was established for the first time by means of supercritical fluid chromatography on chiral polysaccharide column. It was shown that enantiomeric excesses of both E/Z-isomers of (S)-2′-methylbutyrophenone oxime (1S) and (R)-2′-methylbutyrophenone oxime (1R) were equal to 92 ± 2. The cyclopalladation study revealed that while E-isomer is orthopalladated very quickly its Z-counterpart does not enter this reaction. However, upon coordination to Pd(II), Z-oxime slowly isomerizes into E-form with fast subsequent cyclopalladation, so it was possible to perform ortho-palladation of E-oxime in kinetic resolution mode with removal of unreacted Zoxime. Comparatively rare cis-structure of cyclopalladated oxime dimer was proved by means of single-crystal X-ray study. For the first time, it was shown that ortho-palladated chiral oximes behave as enantioselective catalyst in the hydrolysis of chiral esters.

Still Elusive – Pd(II)‐Mediated Base Pairing by an Acetophenone Oxime Palladacycle within 15N‐Labelled Double‐Helical Oligonucleotides

“…The slower‐eluting isomers of the oxime oligonucleotides ON1ao and ON1bo were converted to the respective palladacyclic oligonucleotides ON1ao‐Pd and ON1bo‐Pd by incubation in an aqueous solution of lithium tetrachloropalladate and sodium acetate at 55 °C for 4 d (Scheme 2). Configuration of the oxime double bond of the starting materials was unknown but, according to previous reports, [39] both E and Z isomers eventually react to give the same palladacycle, with the oxime‐OH and the benzene ring trans to each other. RP‐HPLC analysis of the product mixture revealed several new peaks (chromatograms presented in the Supporting Information).…”

C–O Bonds from Pd‐Catalyzed C(sp3)–H Reactions Mediated by Heteroatomic Groups

“…[21] In the absence of the 2,6-disubstitution of the phenyl group, the procedure would probably lead to acetoxylation of the aromatic unit. [25,50] The acetoxylation of the -methine moiety instead of a less hindered -methylene group in the case of exo-and endo-norbornyl-derived alcohols is surprising [Equation (22)]. The skeleton rearrangement of the O-menthyl oxime depicted in Scheme 7 [21,49] is also unusual.…”

“…[65] We suspect that the redox catalytic cycle of the acetoxylation of 8-methylquinolines depends on the procedure. With PhI(OAc) 2 and nitrate or nitrate/O 2 [Equations (48) to (50)], the reaction involves probably Pd III and/or Pd IV intermediates. In contrast, the reaction involving only oxygen as stoichiometric oxidant [Equations (51) and (52)] would imply the Pd II /Pd 0 catalytic cycle.…”

“…In contrast, the reaction involving only oxygen as stoichiometric oxidant [Equations (51) and (52)] would imply the Pd II /Pd 0 catalytic cycle. Comparison of the results obtained under oxygen demonstrates the dependence of the C(sp 3 )-H oxidation on the nature of the catalyst: no reaction in the presence of Pd(OAc) 2 [Equations (48) and (50)] but reaction with 12F or Pd II /pyridinedicarboxylic acid systems [Equations (50) to (52)]. Comparison of the results obtained under oxygen demonstrates the dependence of the C(sp 3 )-H oxidation on the nature of the catalyst: no reaction in the presence of Pd(OAc) 2 [Equations (48) and (50)] but reaction with 12F or Pd II /pyridinedicarboxylic acid systems [Equations (50) to (52)].…”

Selective Binding and Isomerization of Oximes in a Self-Assembled Capsule

“…Oximes ( NOH ) and oxime ethers ( NOMe ) are more stable and undergo isomerization with catalysts (Bronsted or Lewis acids, metal ions, etc.) and thermal or photochemical interventions. − The E- / Z -isomers of NOMe have different physical and chemical properties and play roles in various chemical and biological processes . Furthermore, separation of the E- / Z -isomer of oximes ethers with the highly substituted aryl groups was possible using simple chromatographic techniques, whereas more sophisticated instruments are required for alkyl oxime ethers. − …”