A modified bischler‐napieralski reaction. Synthesis of 2,3,4,9‐ tetrahydro‐1 H ‐pyrido[3,4‐ B ]indole derivatives and their base‐catalyzed transformation to N ‐acetyl‐ N ‐[2‐[1 ‐acetyl‐2‐[1 ‐(acetyloxy)‐1‐propenyl]‐ 1 H ‐indol‐3‐yl]ethyl]acetamides

The treatment of N ‐[2‐(1 H ‐indol‐3‐yl)ethyl]alkanamide, 1 (1), with phosphorus oxychloride under controlled conditions gave l‐alkyl‐2,3,4,9‐tetrahydro‐1 H ‐pyrido[3,4‐ b ]indol‐1‐ol, 2 . The reaction of 2 with acetic anhydride or with methyl isocyanate at room temperature resulted in the formation of amido carbinol 3 and urea carbinol 7, respectively. The former was transformed into amido ester 4 by boiling acetic anhydride. When the reaction of 3 with acetic anhydride was carried out in the presence of excess triethylamine at 105°, C‐N bond cleavage of the tetrahydropyridine ring took place with concurrent bis( N ‐acetylation) to give the enol ester derivative 5 . The structures of all compounds are consistent with chemical and spectral evidence.