ON THE USE OF C-2-SYMMETRICAL AZIRIDINES AS CHIRAL AUXILIARIES

A systematic study has been made of the utility of readily available C -2-symmetric aziridines as auxiliaries for asymmetric alkylation and a ldol reactions of amide enolates. Aziridines with suitably placed oxyg en atoms in the side chains proved to be useful for alkylation reactio ns (d.e. values up to >98%) and the results are explained in terms of an intramolecularly chelated Z-enolate species, which could be observe d directly by means of NMR spectroscopy. In contrast, aziridine auxili aries lacking side-chain oxygens performed better in aldol reactions ( syn selectivity up to 98% d.e.) for which a Zimmerman-Traxler transiti on state is proposed. After reaction, the auxiliaries can be cleaved o ff nondestructively under mild conditions to afford either optically p ure aldehydes or carboxylic acids.