Studies on alkene aziridination using 3-acetoxyaminoquinazolinones.

Oxidation of 3-aminoquinazolinones with lead(IV) acetate in dichloromethane at -20 C gives the corresponding 3-acetoxyaminoquinazolinone. These intermediate 3-acetoxyaminoquinazolinones bring about the aziridination of a wide range of alkenes in good yields. The n.m.r. spectra of these 3-acetoxyaminoquinazolinones shows that there is chirality associated with the acetoxyamino group. Some of the work described in this thesis shows that this chirality arises from retarded rate of inversion at the exocyclic nitrogen on the n.m.r. time scale but that N-inversion at this nitrogen is fast on the time-scale of aziridination. This was accomplished by dynamic n.m.r. spectroscopic studies using 3-aIkoxyaminoquinazolinones and by comparison of diastereoselectivity in inter- and intramolecular aziridination studies using 3-amino-2-(1 -methyl-4-phenylbut-3-en-1-yl) aminoquinazolinone. The remainder of the thesis describes experiments which were designed to show the preferred configuration of the tetrahedral 3-acetoxyamino group in the transition state for aziridination: a knowledge of the location of the acetoxy group on nitrogen was considered a pre-requisite for the rational design of 2-substituted-3-acetoxyaminoquinazolinones for reagent-controlled aziridination of prochiral allcenes. From the preferred sense in diastereoselectivity in the aziridination of 4-substituted-4-hydroxycrotonates and l-substituted-2-methoxycarbonylprop-2-en-1-ols, a mechanism was proposed for aziridination of electron-deficient alkenes which comprises a Michael addition of the acetoxyamino nitrogen to the -position of the alpha,beta-unsaturated ester running ahead of an SN2-type substitution on the acetoxyamino nitrogen by the alkene (see below): this requires an anti relationship between the N-acetoxy group and the quinazolinone carbonyl group. For the analogous phenyl-substituted alkenes, the sense of diastereoselectivity was in agreement with a similar mechanism but with a reversal of the order in which the two aziridine bonds are made (see below) and hence with the requirement for a configuration of the acetoxyamino group syn to the quinazolinone carbonyl group. The application of these models to an aziridination involving double asymmetric induction accounts for the high stereoselectivity using an electron-deficient alkene but low diastereoselectivity using an analogous electron-rich alkene.