The synthesis of medium‐sized cyclic lactams by the intramolecular friedel‐crafts cyclization of isocyanates. Formation of novel pyrazolo[3,4‐c]benzolactams

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Abstract
A series of 4‐ω‐phenylalkyl substituted‐1H‐pyrazol‐5‐amines has been synthesized from the corresponding α‐acetylphenylalkanenitriles and methylhydrazine. They were converted into the corresponding 5‐isocyanates and cyclized under Friedel‐Crafts conditions to medium‐sized cyclic lactams. The reaction was shown to give the 7‐, 8‐, 9‐, and 10‐membered lactams but failed to yield the 11‐membered lactam. Rings synthesized were: pyrazolo[3,4‐c][2]benzazepin‐2(1H)‐one; 10H‐pyrazolo[3,4‐c][2]benzazocin‐10‐one; pyrazolo[3,4‐c][2]benzazonin‐11(1H)‐one; 12H‐pyrazolo[3,4‐c][2]benzazocin‐12‐one.