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Domino Friedel–Crafts‐Type Cyclizations of Difluoroalkenes Promoted by the α‐Cation‐Stabilizing Effect of Fluorine: An Efficient Method for Synthesizing Angular PAHs
Author(s) -
Fuchibe Kohei,
Jyono Hideharu,
Fujiwara Masaki,
Kudo Takao,
Yokota Misaki,
Ichikawa Junji
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201100618
Subject(s) - carbocation , chemistry , friedel–crafts reaction , allylic rearrangement , protonation , ring (chemistry) , fluorine , medicinal chemistry , methylene , domino , regioselectivity , aryl , organic chemistry , catalysis , ion , alkyl
In order to synthesize polycyclic aromatic hydrocarbons with nonlinear arrangements (angular PAHs), acid‐promoted domino cyclizations of 1,1‐difluoroalk‐1‐enes and 1,1‐difluoroalka‐1,3‐dienes were studied. 1,1‐Difluoroalkenes, each bearing two aryl substituents, were regioselectively protonated with FSO 3 H⋅SbF 5 to generate fluorine‐stabilized carbocations, which readily underwent domino Friedel–Crafts‐type cyclizations to give carbocycles based on 6/ n / m /6 ring systems ( n , m =5–7) in good to high yields. Protonation of 1,1‐difluoroalka‐1,3‐dienes took place at their electron‐rich methylene (CH 2 ) carbon atoms in the presence of milder acids such as camphorsulfonic acid and trifluoromethanesulfonic acid. Domino cyclizations of the resulting fluorine‐stabilized allylic carbocations afford carbocycles based on 6/6/6/6 or 6/6/5/6 ring systems in high yields.