
%0 Journal Article
%A Chan, AWK 
%A Crow, WD 
%T Isothiazole chemistry. V. Acylation and acyl migration in 3-hydroxyisothiazole
%J Australian Journal of Chemistry
%D 1968/12/01
%V 21
%N 12
%P 2967-2978
%K 
%R https://doi.org/10.1071/CH9682967
%U https://www.publish.csiro.au/paper/CH9682967 
%X In aprotic solvents acylation of 3-hydroxyisothiazole is subject to kinetic control, leading almost exclusively to the 3-acyloxyisothiazoles. On heating or standing a reversible O &#8594; N migration occurs, the final composition of the mixture depending on the nature of the acyl group. Where aliphatic acyl groups are involved (RCO: R = CH3, C2H5, C3H7, ClCH2, CH3O, C2H5O) the tendency towards migration to nitrogen is inversely related to the size of the group, whereas with aromatic groups (R = C6H5, 4-MeC6H4, 4-NO2C6H5, 3,5-(NO2)2C6H3, C6H5CH2), little or no N-acyl derivative results. Sulphonyl halides lead only to 0-sulphonyl derivatives, which presumably do not rearrange. The migration of the acyl group is shown to be intermolecular, involving both O + O and O &#8594; N migration, by the usual mixed migration experiments, and is catalysed by 3-hydroxyisothiazole and other nucleophiles. The greater thermodynamic stability of the O- or ,N-acyl derivatives, as revealed by equilibrium measurements, is seen to be a function of the steric requirements of the acyl group, the larger groups being more stable on oxygen. Examination of the infrared spectra reveals that this is probably due to out-of-plane twisting in the N-acyl-3- isothiazolones, which prevents N-CO overlap in all derivatives except the formyl which exists as 100% N-formyl at equilibrium. 
