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-tetr ahydropyrrolo[2,1-a]phthalazine (8), prepared by 1,3-dipolar cycloaddition of 2-phenacyl phthalazinium bromide (6a) with acrylonitrile (7a), can be ar omatized by tetrakis-pyridine cobalt (II) dichromate (TPCD) to give 1-cyano -3-benzoylpyrrolo[2,1-a]phthalazine (9a) in good yield. Furthermore, a gene ral and convenient one-pot procedure for preparation of pyrrolo[2,1-a]phtha lazines (9a-p) was developed by 1,3-dipolar cycloaddition of phthalazinium N-ylides (6a-c) with alkenes (7a-g) in the presence of TPCD.