New tetracyclic compounds containing the β‐carboline moiety

Oxidation of 1‐methyl‐3‐methoxycarbonyl‐β‐carboline with selenium dioxide gave 1‐formyl‐3‐methoxycarbonyl‐β‐carboline II . Compound II reacted with acetic or propionic anhydride to give easily the 2‐methoxycarbonyl‐6 H ‐indolo[3,2,1‐ d,e ][1,5]naphthyridin‐6‐ones III ; reaction of II with some primary amines led to the formation of the Schiff bases IV , which were reduced to the 1‐aminomethyl‐3‐methoxycarbonyl‐β‐carbolines V with sodium borohydride. Cyclization of V with aqueous formaldehyde led to the pyrimido[3,4,5‐ lm ]pyrido[3,4‐ b ]indoles VI . Analogously, cyclization with formaldehyde, acetone or 1,1′‐carbonyldiimidazole of the 3‐aminomethyl‐ 1,2,3,4‐tetrahydro‐β‐carbolines VIII , obtained by reaction of 3‐methoxycarbonyl‐1,2,3,4‐tetrahydro‐β‐carboline VII with amines followed by lithium aluminium hydride reduction of the resulting amides, gave the imidazo[1′,5′‐1,6]pyrido[3,4‐ b ]indoles IX and X . Dieckmann cyclization of 3‐methoxycarbonyl‐2‐[(3‐ethoxycarbonyl)‐1‐propyl]‐1,2,3,4‐tetrahydro‐β‐carboline XI led to a 1:1 mixture of the β‐ketoesters XII and XIII , which underwent deethoxycarbonylation to 5,6,8,9,10,11,11a,12‐octahydroindolo[3,2‐ b ]quinolizin‐11‐one XIV . Finally, the polyphosphoric acid (or esters) catalyzed cyclization of the N ‐acyl derivatives XVI of 3‐hydrazinocarbonyl‐β‐carboline XV led smoothly to the 3‐(1,3,4‐oxadiazol‐2‐yl)‐β‐carbolines XVII .