Domino synthesis of fluorine-substituted polycyclic aromatic hydrocarbons: 1,1-difluoroallenes as synthetic platforms.

Rather crafty: 1,1-Difluoroallenes bearing an aryl group and a cyclopentene moiety undergo indium(III)-catalyzed Friedel-Crafts-type cyclization with subsequent ring expansion and dehydrogenation to afford fluorinated polycyclic aromatic hydrocarbons in high yields. The introduction of an Ar group was effected by in situ halogenation of the intermediary indium species and a subsequent Suzuki-Miyaura reaction.

Domino Friedel-Crafts-type cyclizations of difluoroalkenes promoted by the α-cation-stabilizing effect of fluorine: an efficient method for synthesizing angular PAHs.

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.

Facile synthesis of 1,1-difluoroallenes via the difluorovinylidenation of aldehydes and ketones.

2-Bromo-3,3-difluoroallylic acetates were readily prepared by the reaction of carbonyl compounds with 1-bromo-2,2-difluorovinyllithium, generated from 1,1-dibromo-2,2-difluoroethylene, followed by acetylation. On treatment with butyllithium, the bromoacetates underwent selective 1,2-elimination of lithium acetate to afford mono- and disubstituted 1,1-difluoroallenes in high yields.

Activation of 1,1-difluoro-1-alkenes with a transition-metal complex: palladium(II)-catalyzed Friedel-Crafts-type cyclization of 4,4-(difluorohomoallyl)arenes.

Cationic palladium(II) ([Pd(MeCN)4](BF4)2) provides the first transition-metal-catalyzed method for electrophilic activation of electron-deficient 1,1-difluoro-1-alkenes, which allows their Friedel-Crafts-type cyclization with an intramolecular aryl group via a Wacker-type process. By using BF3.OEt2, the cyclization was effected by a catalytic amount of the palladium without its reoxidation.

Friedel-Crafts-type cyclization of 2,2-difluorovinyl ketones via alpha-fluorocarbocations and its application in domino cyclizations.

[Structure: see text] 2,2-Difluorovinyl ketones bearing an aryl group undergo Friedel-Crafts-type cyclization via carbocations stabilized by alpha-fluorines on treatment with a trimethylsilylating agent [Me3SiOTf or Me3SiB(OTf)4]. The reaction affords 4-fluorinated 3-acyl-1,2-dihydronaphthalenes, which are successfully subjected to a substitution-cyclodehydration process or a Nazarov-type cyclization to construct fused polycyclic systems.