Reactivity Of Arylnitrile Oxides And C-Aroyl-N-Phenylnitrones With 3-Methylenedihydro-(3H)-Furan-2-One And Itaconic Anhydride

1,3-dipolar cycloaddition is a powerful route for the synthesis of five-membered heterocycles. The [3+2] cycloadditions of some alpha-methylene-gamma-buryrolactones, namely 3-methylenedihydro-(3H)-furan-2-one (1) and itaconic anhydride (2) were Studied. Their reactions with arylnitrile oxides (3) and Caroyl-N-phenylnitrones (7) proceed with complete regioselectivity. From a stereochemical point of view, the addition of arylnitrile oxides (3) leads to the unique spiroheterocycles (4-5). Actually, a single stereocenter is generated during the reaction. In the particular case of p-nitrophenylnitrile oxide (3d), only the diacidic form (10d) of the spiroheterocyle (5d) was isolated. In contrast, the addition of C-aroyl-N-phenylnitrones (7) produces a couple of diastereoisomers. since two stereocenters are generated simultaneously. Nevertheless, the reaction is regioselective and stereospecific leading also to the single spiroheterocycles (1920). The proposed stereochemistry of spiranic compounds (19d) and (20d) has been corroborated by two single crystal X-ray crystallographic analysis.