Preparation of pyrrolo[3,2,1‐ jk ]carbazole by nickel(0) mediated ring contraction of pyrrolo[3,2,1‐ kl ]phenothiazine. Proton NMR and mass spectral studies

Pyrrolo[3,2,1‐ jk ]carbazole 1a , the previously unreported 16π‐electron parent compound, has been synthesized by treatment of pyrrolo[3,2,1‐ kl ]phenothiazine 2a with a 1:1 mixture of bis(1,5‐cyclooctadiene) nickel(0) and 2,2′‐bipyridyl. An unequivocal assignment of the 1 H nmr spectrum of 1a was made by decoupling experiments and by comparison with the 1 H nmr spectrum of 1,9‐dideuteriopyrrolo[3,2,1‐ jk ]carbazole 1b . Metastable ion studies, exact mass measurements and the dideuterioderivative 1b were utilized to investigate the electron impact induced fragmentation of 1a .