Synthesis of 1‐arylacenaphtho[1,2‐ d ]pyrazoles and 5,7‐Dehydro‐5 H ,7 H ‐benzo[ b ]acenaphtho[1,2‐ e ]‐1,3a,6a‐triazapentalenes

2‐Benzoyl‐ 5 and 2‐acetylacenaphthenone 6 , prepared from the corresponding 1‐acyl‐2‐(1‐pyrrolidinyl)‐acenaphthylenes 2 and 3 , reacted with arylhydrazines 8 under acidic conditions to give the corresponding 1‐arylacenaphtho[1,2‐ d ]pyrazoles 9 and 10 . Novel heteropentalene mesomeric betaines, 5,7‐dehydro‐5 H ,7 H ‐benzo[ b ]acenaphtho[1,2‐ e ]‐1,3a,6a‐triazapentalenes 13 and 14 were prepared by reductive cyclization of 1‐( o ‐nitrophenyl)acenaphtho[1,2‐ d ]pyrazoles 9d and 10d , respectively.