CHIRAL AMINALS - POWERFUL AUXILIARIES IN ASYMMETRIC-SYNTHESIS

Chiral aminals are prepared from chiral C2 symmetrical diamines and al dehydes. The chiral imidazolidine ring exerts its stereocontrol either through steric or chelation effects. Reaction of aqueous glyoxal with diamine 1 results in a new chiral synthon 6; this ''chiron'' is a use ful precursor for alpha-hydroxy aldehydes and for alpha-amino aldehyde s. An aminal of nicotinaldehyde 7 reacts stereoselectively with organo copper reagents to afford a chiral dihydropyridine, which is a startin g point for several shea asymmetric syntheses of indolo- and benzo-qui nolizine alkaloids.