Rearrangements of 4‐(2‐Aminophenyl)‐1,4‐dihydro‐2,6‐dimethyl‐3,5‐pyridinedicarboxylic acid diethyl ester

The treatment of 4‐(2‐aminophenyl)‐1,4‐dihydro‐2,6‐dimethyl‐3,5‐pyridinecarboxylic acid diethyl ester (III) with refluxing toluene or pyridine afforded 1,2,3,6‐tetrahydro‐2,4‐dimethyl‐2,6‐methano‐1,3‐benzodiazocine‐5,11‐dicarboxylic acid diethyl ester (IV) as the major product. In addition, the following minor products were isolated: 2‐methyl‐3‐quinolinecarboxylic acid ethyl ester (V), 3‐(2‐aminophenyl)‐5‐methyl‐6‐azabicyclo[3,3,1]‐hept‐1‐ene‐2,4‐dicarboxylic acid diethyl ester (VI), and 5,6‐dihydro‐2,4‐dimethyl‐5‐oxobenzo[ c ][2,7]naphthyridine‐1‐carboxylic acid ethyl ester (VII). In contrast, acidic conditions caused the conversion of III into V in a 95% yield. The formation of the latter appears to involve IV as an intermediate, since IV degraded rapidly in acid to give V in a quantitative yield.