A new cyclization to fused pyrazoles tunable for pericyclic or pseudopericyclic route: an experimental and theoretical study.
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).
Filák
László
L
Chemical Research Center, Hungarian Academy of Sciences, Budapest, Hungary.
Rokob
Tibor András
TA
Vaskó
Gyöngyvér Agnes
GA
Egyed
Orsolya
O
Gömöry
Agnes
A
Riedl
Zsuzsanna
Z
Hajós
György
G
D003198:Computer Simulation; D003500:Cyclization; D008958:Models, Molecular; D015394:Molecular Structure; D011720:Pyrazoles / Q000138:chemical synthesis* / Q000737:chemistry; D011789:Quantum Theory; D013237:Stereoisomerism
D011720:Pyrazoles