Two 5-oxa-2,6-diazaspiro[3.4]octan-1-one derivatives from the [3+2] cycloaddition of methylenelactams with nitrones

The two title 5-oxa-2,6-diazaspiro[3.4] octan-1-one adducts, 7-benzoyl-2-(4 -methoxyphenyl)-6-phenyl-5-oxa-2,6-diaza spiro[3.4]octan-1-one, C25H22N2O4, (III), and 6-tert-butyl-2-(4-methylphenyl)-7-phenyl-5-oxa-2,6-diazaspiro [ 3.4] octan-1-one, C22H26N2O2, (IV), were obtained from a stereospecific [32] 1,3-cycloaddition of 3-methylene azetidin-2-ones as dipolarophiles with nitrones. The lactam ring is conjugated with the p-methoxyphenyl or p-methy lphenyl moiety. The envelope conformations of the isoxazolidine rings in (I II) and (IV) are different, leading the substituents to be pseudo-axial in (III) and pseudo-equatorial in (IV).