Reactions of the nitrones− O+ N (Me) C (H) Ar 1 (Ar= phenyl 1a, 4-methylphenyl 1b, 2, 4, 6- trimethylphenyl 1c, and anthracen-9-yl 1d) with the cyclic β-diketones 1, 3-indandione 2 or barbituric acid 3 in CH2Cl2, afford the corresponding endiones 2′ a–2′ d or 3′ a–3′ d. In contrast, dimedone 4 reacts with 1a or 1b to give the endione 4′ a or 4′ b and the bis- adduct 4 ″a or 4 ″b. Nevertheless, reaction of 4 with 1c or 1d in CH2Cl2 furnishes only ...