title: A new cyclization to fused pyrazoles tunable for pericyclic or pseudopericyclic route: an experimental and theoretical study.
abstract: 2-Pyrazinyl (2) and 3-pyridazinylketone arylhydrazones (6) and their benzologues undergo a ring closure reaction to yield pyrazolo[3,4- b]pyrazines (4) and pyrazolo[4,3- c]pyridazines (7), respectively, in acceptable to good yields. The reaction was found to be accelerated by using acidic or basic conditions. Quantum chemical calculations suggest the key step of the mechanism to be a direct cyclization; analysis of aromaticity based on computed magnetic properties revealed its medium-dependent pericyclic or pseudopericyclic character. The cyclization reaction has also been extended for the synthesis of related ring systems ( 9, 12, 14).
authors.affiliation: Chemical Research Center, Hungarian Academy of Sciences, Budapest, Hungary.
authors.forename: László
authors.initials: L
authors.lastname: Filák
authors.forename: Tibor András
authors.initials: TA
authors.lastname: Rokob
authors.forename: Gyöngyvér Agnes
authors.initials: GA
authors.lastname: Vaskó
authors.forename: Orsolya
authors.initials: O
authors.lastname: Egyed
authors.forename: Agnes
authors.initials: A
authors.lastname: Gömöry
authors.forename: Zsuzsanna
authors.initials: Z
authors.lastname: Riedl
authors.forename: György
authors.initials: G
authors.lastname: Hajós
mesh_terms: D003198:Computer Simulation; D003500:Cyclization; D008958:Models, Molecular; D015394:Molecular Structure; D011720:Pyrazoles / Q000138:chemical synthesis* / Q000737:chemistry; D011789:Quantum Theory; D013237:Stereoisomerism
chemical_list: D011720:Pyrazoles