(-)-(1R,5R)-6-tert-butoxycarbonyl-2-oxa-6-azabicyclo[3.3.0]octan-3-one

(4R,5R)-5-allyl-3-tert-butoxycarbonyl-4-tert-butoxycarbonylmethyl-2-oxazolidinone

(1R,5R)-(-)-6-aza-6-benzyloxycarbonyl-2-oxabicyclo[3.3.0]octan-3-one

((2R,3R)-2-Allyl-5-oxo-tetrahydro-furan-3-yl)-carbamic acid tert-butyl ester

(4R,5R)-5-allyl-4-tert-butoxycarbonylmethyl-2-oxazolidinone