ChemInform Abstract: AZOLE, MECHANISMUS DER EINWIRKUNG VON HYDROXYLAMIN AUF MESITYLOXID

Hydration of 2-Isoxazoline Leading to a Stable 3,5,5-Trisubstituted 3-Isoxazolidinol − N-Acylated Derivatives and Ring-Chain Tautomerism Study

“…Formation of 3,5,5-trimethyl-2-isoxazoline from mesityl oxide and hydroxylamine under anhydrous basic conditions (MeONa/MeOH) was found to occur through 3-isoxazolidinol A, in equilibrium with openchain tautomer AЈ (path ii, R ϭ RЈ ϭ RЈЈ ϭ Me). [6] Path (i) in Scheme 3 is an alternative way of accessing 3-isoxazolidinols. These derivatives had only been previously obtained from α,β-unsaturated carbonyl compounds.…”

“…Dehydration of 5 occurred at 100°C, in marked contrast with its trimethyl analog mentioned above, which could only be observed by 1 H NMR at Ϫ40°C (its dehydration started at Ϫ20°C). [6] Actually, there is only one previous report in the literature on isolable N-unsubstituted 3-isoxazolidinols A [R ϭ H, RЈ ϭ Ph; R" ϭ HOC(CH 2 ) 5 or HOCMe 2 , mixture of diastereomers according to 1 H NMR]. [8] A common possible explanation for this unusual stability might be the steric hindrance of the bulky substituent at C-3 along with stabilizing intermolecular hydrogen bonds between 3-OH or NH and the carbonyl (hydroxy) groups present in the side-chain.…”