organic compounds
The crystal structures of trans-phenyl 2-phenyl-1,6-dioxa-2-azaspiro[4.4]non-3-yl ketone, C19H19NO3, and (3,3a,6a)-hexahydro-2-phenylfuro[3,2-d]isoxazol-3-yl phenyl ketone, C18H17NO3, are reported. In both compounds, the isoxazolidine rings adopt envelope conformations in which the O atom is bent out of the approximate plane of the other four ring atoms. Modest to negligible endo selectivities were confirmed in 1,3-dipolar cycloadditions of benzoylmethyleneaniline N-oxide with enol ethers.