A variety of oxazole derivatives that possess an alpha,beta-unsaturated substituent at the 2-position were conveniently synthesized in good yields via a Hantzsch-type reaction between dehydroamino acid amides and P-bromopyruvate derivatives. Furthermore, oxazoles with substituents at the 2- and 5-positions were also obtained in good yields using the corresponding beta-substituted beta-bromopyruvate derivatives. A revised reaction mechanism to explain the enhanced reactivity of dehydroamino acid amides for the Hantzsch-oxazole-type reaction is presented.
of racemic β-halo-α-keto esters through carbonyl-enereaction were realized using a chiral N,N′-dioxide-nickel(II) complex, giving the corresponding β-halo-α-hydroxy esters containing two vicinal chiral tri- and tetrasubstituted carbon centers in good yields and dr with excellent ee values without the use of extra bases. Meanwhile, a proposed reactionmechanism was presented according to the configuration