Abstract
Dry distillation of acetyl and benzoyl derivatives (I) of o-aminophenylacetic acid with equal amount of soda lime affords 2-methyl-and 2-phenyl-indole (II) in 66 and 59% yield, respectively, but the same reaction of N-acetyloxindole (III) failed to give 2-methylindole, resulting in recovery of the starting material. Similarly, 2-methyl-and 2-phenyl-dihydroquinoline (VI and VII) was obtained in 66% and 57% yield, respectively, from acetyl and benzoyl derivative (V) of o-aminophenylpropionic acid. Catalytic dehydrogenation of (VI) or (VII) over palladium-asbestos in safrole easily gave the corresponding quinoline compounds, but the acetyl compound (IX) of o-aminocinnamic acid failed to undergo cyclization to the corresponding quinoline compounds (VII). This is probably due to the trans configuration of (IX).
The structure of 2-R-dihydroquinoline derivatives here formed, whether it is represented by (VI) or (VII), was examined from infrared and ultraviolet spectral data. Compounds with a substituent with -I effect, such as methyl, in α-position, are mainly of α, β-enamine type (VII) with distinctly positive Liebermann reaction but on allowing to a, β-enamine type (VII) with distinctly positive Liebermann reaction but on allowing to stand over night with dilute hydrochloric acid or on warming for a short time, the Liebermann reaction becomes negative. Derivatives with electrophilic substituent, like phenly, are all azomethine type (VI) and are negative to Liebermann reaction. The salts of (VII), such as perchlorate, form immonium salt.
