Neue Reaktionen in der Isatin‐Reihe, II. Das 2‐Hydroxy‐1.4‐dihydro‐chinolinsystem

Die 3-Dicyanmethylen-oxindole 3 a – d bilden mit Diazomethan O-Methylderivate des bisher unbekannten, durch Konjugation stabilisierten 2-Hydroxy-1.4-dihydro-chinolinsystems (6 a – c). Ahnlich wird aus 3 a und Phenyldiazomethan das 2-Hydroxy-1.4-dihydro-chinolin-derivat 5 d gebildet, das trotz der formalen Tautomeriemoglichkeit praktisch nur als Enol vorliegt. Dagegen liefert 6 a bei saurer Hydrolyse die Carbostyril-4-essigsaure 7, fur die infolge des Konjugationsverlusts eine stabile Enolstruktur nicht moglich ist. New Reactions in the Isatin Series, II The 2-Hydroxy-1.4-dihydroquinoline System The 3-(dicyanomethylene)oxindoles 3 a – d react with diazomethane to give O-methyl derivatives of the hitherto unknown 2-hydroxy-1.4-dihydroquinoline system (6 a – c); these are stabilized by conjugation. Similarly, 3 a yields with phenyldiazomethane the 2-hydroxy-1.4-dihydroquinoline derivative 5 d, which exists practically entirely in the enol form, although it is formally able to tautomerize. In contrast, 6 a is hydrolized by acid to yield carbostyril-4-acetic acid 7, for which no stable enolic structure is possible owing to the loss of conjugation.