Christopher G. Watson

E–Z-isomerism in aldimines

A range of ortho-disubstituted C-aryl aldimines has been synthesized. N.m.r. spectroscopic analysis revealed a significant proportion of the Z-isomer at equilibrium in solution. The E–Z-isomer distribution is critically examined in terms of electronic, steric, and solvent effects. The effect of trace amounts of carboxylic acid on imine stereomutation is discussed.

Species-strain dependence of stereoselectivity in microbial oxidation of thioethers

Abstract The stereoselectivity in the aerobic, microbial oxidation of thioethers and sulphoxides is shown to be dependent on species and strain. A strain of Aspergillus niger was used to obtain an optically active dialkyl sulphoxide.

Equilibrium distribution of E–Z-ketimine isomers

The ratio of E–Z-imine isomers at equilibrium is dependent on resonance stabilization, non-bonding interactions, substitution, and solvent. Stereochemical assignments are based upon i.r. and n.m.r. data.

Dynamic stereochemistry of imines and derivatives. Part VI. Stereochemistry of the peroxyacid–imine route to oxaziridines

The stereochemistry of the peroxyacid oxidation of N-alkyl-aldimines and -ketimines to oxaziridines containing a stable nitrogen pyramid is considered over a range of reaction conditions. The possible relevance of reactant and product molecular geometry in distinguishing between the concerted and stepwise mechanisms is discussed. A comparison is made between rate constants of several peroxyacid oxidation reactions in different solvents. The concerted mechanism appears to be less attractive on the basis of stereochemical and solvent effect data.

Monooxygenase-catalysed metabolism of thioethers and selenoethers by fungi

Abstract Evidence for mono-oxygenase activity during the metabolism of thioethers by the fungus Aspergillus niger is presented. Attempts to obtain selenoxides as microbial metabolic products are described.

Mechanism of aromatic hydroxylation in fungi. Evidence for the formation of arene oxides

Aromatic and aliphatic hydroxylations as well as O-demethylations occurred during metabolism of aromatic substrates by a range of fungi. para-Hydroxylation of monosubstituted aryl rings by fungi proceeded with migration and retention of deuterium label (NIH shift) and appeared to involve only arene 3,4-oxide intermediates, in common with plant and animal metabolism. The possibility of contributions from arene 1,2- or 2,3-oxide intermediates during ortho-hydroxylation is examined in the light of the results of oxygen-18 incorporation, the lack of deuterium–hydrogen primary kinetic isotope effects, and the wide range of deuterium migration and retention values. From these last experimental data no evidence for an arene oxide isomerase enzyme was found.