Synthesis of new guanidine derivatives from 2′,3′,4′,9′‐tetrahydrospiro[piperidine‐4,1′‐[1 H ]pyrido[3,4‐ b ]indole]

The reaction of the isothiourea derivative 2 with methylaminc or pyrrolidine resulted in guanidines 3a‐3b . Using hydrazine under the same conditions the tetrazole derivative 4 was obtained. On reacting 2 with piperidine, morpholine, methylhydrazine, phenylhydrazine, hydroxylamine or sodium hydroxide, cycliza‐tion took place leading to the novel 4‐cyanimino‐1,2,3,4,6,7,12,12b‐octahydro‐3,12b‐ethanopyrim‐ido[1′,6′:1,2]pyrido[3,4‐ b ]indole ( 5 ). Some structural aspects of 5 and other model compounds were analysed mainly by 13 C nmr spectroscopy.