Chiral glycine cation equivalents: N-acyliminium species derived from diketopiperazines
Bull SD., Davies SG., Christopher Garner A., O'Shea MD., Savory ED., Snow EJ.
Studies towards a N, N′-bis(p-methoxybenzyl)diketopiperazine asymmetric glycine cation equivalent for the synthesis of homochiral α-amino acids are described. The oxidation of enolate 3 with molecular oxygen provides either a mixture of hydroxylated diketopiperazines 7 and 8 or trione 10 depending upon the reaction conditions. The nucleophilic reduction of trione 10 and the reaction of acetoxy N-acyliminium ion precursors 5 and 6, derived from 7 and 8, with allyltrimethylsilane and boron trifluoride etherate is examined and a model for the stereoselectivity observed in these additions is presented. © 2002 The Royal Society of Chemistry.