On the electronic structure of some mono- and bisoxazolines

Abstract

He(I) photoelectron (PE) spectra of 2-methyl-4,5-dihydro -1,3-oxazole 1, 4-(tert-butyl)-2-{[4-(tert-butyl)-4,5-dihydro-1,3-oxazol-2-yl]methyl}-4,5-dihydro-1,3-oxazole 2, 4- and N-[2-(4-isopropyl-4,5-dihydro-1,3-oxazol-2-yl)phenyl]-N,N-diphenylamine 10 have been recorded and their valence electronic structures analysed using quantum chemical ab initio and/or PM3 calculations. Also, a discussion of IR, UV spectra and a correlation of 13 C NMR chemical shifts with total atomic charges are presented.

A First Case of Asymmetric Catalysis Induced by Metal‐Free Bisoxazolines

“…In contrast, the bisoxazolines seem to adopt a planar conjugated form in the monoprotonated state exhibiting two hydrogen‐bond donor and two acceptor sites: upon addition of one equivalent of trifluoroacetic acid to compound 8d , a strong absorption band around 280 nm occurs (see Supporting Information) demonstrating the enamine‐imine conjugation, which has been observed previously in bisoxazoline–metal complexes12 and structurally related semicorrins 13. Photoelectron spectra of neutral bisoxazolines also indicate the presence of conjugated tautomers in the gas phase 14. This parallels the behaviour of monocationic bisamidine 1 as shown in Scheme .…”

Structural and Chiroptical Properties of Acyclic and Macrocyclic 1,5-Bis(oxazoline) Ligands and Their Copper(I) and Silver(I) Complexes

“…The short‐wavelength band (λ max = 194 nm) can be assigned to the π C=N −π* C=N transition in C 2 ‐symmetric 1e , whereas in 1d it (λ max = 190 nm) comprises superimposed 1 L a bands of the phenyl chromophore. The weak long‐wavelength band at λ max = 264 nm in the UV spectrum of 1e is assigned to the conjugated π−π* transition, based on the ab initio 6‐31G* calculations and analysis of photoelectronic spectra;49 1a and 1b show similar UV spectra. However, the spectrum of 1d is strikingly different showing much less intense bands at 264, 258, and 252 nm corresponding to phenyl substituents.…”

Asymmetric Cyclopropanation of Vinyl Fluorides: Access to Enantiopure Monofluorinated Cyclopropane Carboxylates

“…24 While the enantioselectivity of the organometallic ligand is determined by the chiral topology of the catalytic complex, its electronic structure is responsible for the completion of the catalytic cycle. 25 The enantiopure bis(oxazolines) 11 and 12 were synthesized according to published procedures 22,26 from the corresponding amino alcohols, which are readily available from the corresponding amino acids. 27 The enantiopure catalysts were formed in situ by mixing the bis(oxazoline) ligand with a stoichiometric amount of CuOTf•½benzene and used in an amount of 2 mol%.…”