Studies on tertiary amine oxides. LXXV. Reactions of aromatic N-oxides with Meldrum's acid in the presence of acetic anhydride.

Abstract

Reactions of quinoline, lepidine, 4-chloro-, 4-methoxy- and 4-morpholino-quinoline 1-oxides (1a-e) with Meldrum's acid (2) in acetic anhydride smoothly occurred at room temperature to afford the corresponding 5-(2-quinolyl)-Meldrum's aoids (3a-e) in good yields. On the other hand, when the reactions were carried out in dimethylformamide containing 1.2 eq acetic anhydride the N-ylides (4a-e) were produced ; while the reactions of 1a, d, e yielded only N-ylides 4a, d, e, 4b, c were formed along with smaller amounts of 3b, c in the reactions of 1b, c. 3-Bromoquinoline 1-oxide (1f) gave only the N-ylide (4f) and isoquinoline 2-oxide (6) gave the 1-substituted isoquinoline (7) independently of the reaction conditions. Further, 5-alkyl-Meldrum's acids (8a-c) also reacted readily with 1a in acetic anhydride to give the corresponding 2-substituted quinolines (9a-c) in good yields. Heating of 3a, b with conc. hydrochloric acid, 10% hydrochloric acid or methanol containing 10% hydrogen chloride gave 2-methylquinolines (10a, b), 2-quinolineacetic acids (11a, b) or their methyl esters (12a, b), respectively. Similarly, 9a-c afforded 2-alkylquinolines (14a-c) in good yields upon being refluxed with conc. hydrochloric acid.