Tetracyclic azetidinones 8 , 9 and 12 – 17 were synthesized. In the cases of 8 and 9 , the main component was isolated from the two-component product of the cycloaddition. The minor component was concentrated to give a mixture, from which a computer technique utilizing the known spectrum of the main component gave the proton resonance spectrum also of the minor component. Only one diastereomer could be isolated for the each of the analogues 12 – 17 . Reaction of the 1,3-oxazine 3 with chloroacetyl chloride gave, besides the azetidinone 12 , the 1,3-oxazine [2,3- b ]-1,3-oxazin-4-one derivative 18 . Configurations and conformations were determined by IR, 1H and 13C NMR spectroscopy.