Aziridines. 77 - cis-trans pair of a N-benzoylaziridine: Dependence of carbonyl reactivity on nitrogen pyramid

In a multistep process, anthracenide and both 1-benzoyl-2-methyl-3-phenylaz iridines 1a form carbanion 4a that abstracts a proton from the solvent THE The steep N pyramid of cis-1a makes attack of 4a on C=O of cis-1a fast enou gh to compete with proton abstraction while C=O of trans-1a with its flat a nd rapidly inverting pyramid did not react with 4a. The initially generated ketyls of la show another cis-trans effect of steric repulsion: their homo lytic ring opening forms benzylic radical 3a, the precursor of carbanion 4a , but this opening is regiospecific for the cis ketyl only. The trans ketyl forms some isomeric radical too.