Abstract
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 beta-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 '' h. Nevertheless, reaction of 4 with 1c or 1d in CH2Cl2 furnishes only the endione adducts 4'c or 4'd. However, the reaction of 4 with 1a or 1b in methanol gives only 4 '' a or 4 '' b, respectively. Among acyclic beta-diketones only malonic acid 7 reacts with 1a-1c. Reaction of 7 with 1a in CH2Cl2 forms cinnamic acid 7 '' a, whereas in the case of 1b, the endione 7'b and (E)-3-p-tolylacrylic acid 7 '' b are obtained. The nitrone 1c reacts with 7 in CH2Cl2 to afford the endione 7'c or with acetone yielding (E)-4-mesitylbut-3-en-2-one 8. X-ray analyses are reported for 4'c, 5, and 7 '' b. In addition, the calculated acidity of the hydrogen at the alpha-C atom is shown to correlate with the reactivity of the beta-diketones with nitrones. (C) 2012 Elsevier Ltd. All rights reserved.