Synthesis of pyrrolo[2,1‐ a ]phthalazines by 1,3‐dipolar cycloaddition of phthalazinium N ‐ylides with alkenes in the presence of tetrakis‐pyridine cobalt (II) dichromate

We describe here, for the first time, that 1‐cyano‐3‐benzoyl‐1,2,3,10b‐tetrahydropyrrolo[2,1‐ a ]phthalazine (8), prepared by 1,3‐dipolar cycloaddition of 2‐phenacyl phthalazinium bromide ( 6a ) with acrylonitrile ( 7a ), can be aromatized by tetrakis‐pyridine cobalt (II) dichromate (TPCD) to give 1‐cyano‐3‐benzoylpyrrolo[2,1‐α]phthalazine ( 9a ) in good yield. Furthermore, a general and convenient one‐pot procedure for preparation of pyrrolo[2,1‐α]phthalazines ( 9a‐p ) was developed by 1,3‐dipolar cycloaddition of phthala zinium N ‐ylides ( 6a‐c ) with alkenes ( 7a‐g ) in the presence of TPCD.