N-ALKYLOXYCARBONYL-3-ARYLOXAZIRIDINES - THEIR PREPARATION, STRUCTURE,AND UTILIZATION AS ELECTROPHILIC AMINATION REAGENTS

This paper reports the synthesis of a series of N-protected oxaziridin es (N-Moc, Boc, Z or Fmoc) and discusses their ability to deliver thei r N-alkoxycarbonyl fragment to amines, enolates, sulfur, and phosphoru s nucleophiles (electrophilic amination). These oxaziridines are prepa red by oxidation of the corresponding imines with oxone or anhydrous M CPBA lithium salt as the source of oxygen. They transfer their N-prote cted fragment to primary and secondary amines to give protected hydraz ines in fair to excellent yield. The nitrogen transfer to free amino a cids (in form of their R4N+ salts) is particularly fast, even at low t emperature, providing L (or D) N-protected alpha-hydrazino acids. Enol ates are C-aminated to give N-protected alpha-amino ketones, esters, o r amides in modest yield, due to a side aldol reaction of the unreacte d enolate with the released benzaldehyde. With tertiary amines (Et3N), sulfides (PhSMe), and phosphines (Ph3P), amination and oxidation proc eed in a parallel way; the amount of amination product increases when the temperature is lowered (kinetic control). Some of the factors that can orient the oxaziridine reactivity towards amination or oxidation of nucleophiles are considered.