2′,3′,4′,9′‐Tetrahydrospiro[cyclohexane‐1,1′‐(1 h )pyrido[3,4‐ b ]indol]‐2‐ones and their transformations into 2,3,4,4a,5,6,9,14‐octahydro‐4a‐hydroxy‐1 h ,8 h ‐pyrido[3,4‐ b :2,1‐ i' ]diindole‐5‐carbonitriles and 5‐substituted 2,3,4,4a,9,14‐hexahydro‐4a‐hydroxy‐1 H ,8 H ‐indolo[2′,3′:3,4]‐pyrido[1,2‐ c ]benzimidazol‐6‐(5 H )ones

The condensation of 1 H ‐indol‐3‐ethanamine derivatives 1 with 1,2‐cyclohexanedione ( 2 ) and subsequent transformation of the resulting 2‐[[2‐(1 H ‐indol‐3‐yl)ethyl]imino]cyclohexanones ( 3 ) into 2′,3′,4′,9′‐tetrahydrospiro[cyclohexane‐1,1′‐(1 H )pyrido[3,4‐ b ]indol]‐2‐ones 4 using Pictet‐Spengler reaction conditions is described. The reaction of 4 with acrylonitrile gave a mixture of pentacyclic derivatives, 2,3,4,4a,5,6,9,14‐octahydro‐4a‐hydroxy‐1 H ,8 H ‐pyrido[3,4‐ b :2,1‐ i' ]diindole‐5‐carbonitriles 12 . Treatment of 4 with alkyl and aryl isocyanates ( 14 ) at room temperature gave 5‐substituted‐2,3,4,4a,9,14‐hexahydro‐4a‐hydroxy‐1 H ,8 H ‐indolo[2′,3′:3,4]pyrido[1,2‐ c ]benzimidazol‐6‐(5 H )ones 16 . Dehydration of 16 gave 5‐substituted‐2,3,9,14‐tetra‐hydro‐1 H ,8 H ‐indolo[2′,3′‐3,4]pyrido[1,2‐c]benzimidazol‐6‐(5 H )ones ( 17 ). Spectral and chemical evidence is presented to confirm structures 4, 12, 16 , and 17 .