Scope and Limitations of a Modified Hantzsch Reaction for the Synthesis of Oxazole-Dehydroamino Acid Derivatives from Dehydroamino Acid Amides

A variety of oxazole derivatives that possess an ,-unsaturated substituent at the 2-position were conveniently synthesized in good yields via a Hantzsch-type reaction between dehydroamino acid amides and -bromopyruvate derivatives.Furthermore, oxazoles with substituents at the 2-and 5-positions were also obtained in good yields using the corresponding -substituted -bromopyruvate derivatives.A revised reaction mechanism to explain the enhanced reactivity of dehydroamino acid amides for the Hantzsch-oxazole-type reaction is presented.[a] Ph 3 P, DEAD/THF MnO 2 /benzene [b] K 3 PO 4 , Tf 2 O, Ph 2 SO/CH 2 Cl 2 or Scheme 1.