methyl 2-(N-Boc)amino-3-bromo-2-butenoate

(4S,5R)-tert-butyl 4-carbamoyl-2,2,5-trimethyloxazolidine-3-carboxylate

(4S,5R)-tert-butyl 4-carbamothioyl-2,2,5-trimethyloxazolidine-3-carboxylate