Diene-derived N-(3,4-Dihydro-4-oxoquinazolin-3-yl)aziridines : preparation and reactivity

The reaction of naphthalene with 3-acetoxyamino-2-alkylquinazolinones (QNHOAc) in the presence of hexamethyldisilazane (HMDS) gave a mixture of mono- and bis-aziridines in a ratio which depends upon the bulk of the (Q)2-substitutent. By following the aziridination by NMR spectroscopy it was concluded that the first formed aziridine was the endo-N-invertomer and that bis-aziridination occurred only after N-inversion to the exo-N-invertomer. In the absence of HMDS the corresponding bis-aziridine is the major product. O6NHOAc [Q6 = 2 (S)-(2,2-dimethyl-1-hydroxypropyl)quinazolin-4(3H)-one] was found to convert cyclopentadiene, 1,3- and 1,4-cyclohexadiene and cycloheptadiene into the corresponding N-(Q6)-aziridines in the presence of titanium(IV) tert-butoxide with complete or high diastereoselectivity. Accompanying these aziridines in the case of 1,3- and 1,4-cyclohexadiene were N-(Q6)-substituted dienylamines formed with complete diastereoselectivity by formal insertion into the (bis)allylic carbon hydrogen bonds. In ring-opening of the 1,3-cyclohexadiene-derived aziridine above (two diastereoisomers) by mild acid, formation of the alcohol product involves participation by the Q6-carbonyl oxygen. Cyclisation of each of these alcohols with carbonyl diimidazole and N-Q6 bond reduction using samarium(II) iodide gave the corresponding oxazolidinones in enantiopurified form.;The electron-withdrawing effect of the quinazolinone ring activates N-(Q)-aziridines towards attack by nucleophiles including thiolate and selenolate in the absence of acid. Several factors were found to influence regioselectivity in ring-opening of N-(Q)-aziridine-2-carboxylic esters at C2 including co-ordination of the aziridine to samarium(III) ion and overlap of the C-N sigma anti-bonding orbital with the carbonyl pi anti-bonding orbital. (Q)2-Trifluoromethyl-substituted aziridines undergo ring-opening at a faster rate due to increased stabilisation of the nitrogen anion intermediate.