Et3B- and Et2Zn-Mediated Radical Additions to Glyoxylate Imines, Compared Stereoinductions

1,3-Stereoinduction in the addition of alkyl radicals to glyoxylic imines derived from various chiral amines has been investigated. New synthetic methodologies involving Et3B and Et2Zn as mediators have been compared. Dihydro-1,4-oxazin-2-one (2b) gave the highest d.e. but no chemoselectivity. Open chain analogues derived from β-alkoxyamines led to good stereoinduction when the reaction was performed with Et2Zn which is a bidentate complexing reagent.