Opening of the four-membered ring in perfluorinated 1-alkyl-2-phenyl- and 1-aryl-1,2-dihydrocyclobutabenzenes in the system I2-SbF5

Abstract

Reactions of perfluorinated 1-phenyl-, 1-(2-ethylphenyl)-, 1-(4-ethylphenyl)-, 1-methyl-2-phenyl-, and 1-ethyl-2-phenyl-1,2-dihydrocyclobutabenzenes with iodine in antimony pentafluoride at 130°C, followed by hydroysis of the reaction mixture, resulted in the formation of perfluorinated 2-methyl-, 2-ethyl-2′-methyl-, 4-ethyl-2′-methyl-, 2-ethyl-, and 2-propylbenzophenones via opening of the four-membered ring in the initial cyclobutabenzene at the C 1 -C 2 bond. The presence of hydrogen fluoride facilitates the process and promotes profound transformations leading to anthracene derivatives.We previously showed that dimerization of perfluoro(1,2-dihydrocyclobutabenzene) (I) in SbF 5 and reactions of compound I, perfluoro(1-methyl-1,2-dihydrocyclobutabenzene) (II), and perfluoro(1-ethyl-1,2-dihydrocyclobutabenzene) (III) with Br 2 or HF in the presence of SbF 5 involve opening of the four-membered ring at the C arom -C 2 bond with formation of the corresponding 2-X-perfluoro(alkylbenzenes) [X = perfluoro(1,2-dihydrocyclobutabenzen-1-yl, Br, H] [1-3]. In contrast, opening of the four-membered ring in compound I in the system I 2 -SbF 5 occurs at both C arom -C 2 and C 1 -C 2 bonds, leading to 1,2,3,4-tetrafluoro-5-iodo-6-(perfluoroethyl)benzene together with perfluoro(o-xylene) (IV) [4]. However, no iodo derivatives were formed in analogous reactions of cyclobutabenzenes II and III, and the major products were the corresponding perfluoro(1,2-dialkylbenzenes) [5].With a view to elucidate how the nature of perfluorinated substituents in the four-membered ring of perfluorinated 1,2-dihydrocyclobutabenzenes affects

Formation of fluorene and anthracene derivatives in reactions of perfluorinated 1-alkyl-1-phenyl- and 1-alkyl-2-phenyl-1,2-dihydrocylobutabenzenes with antimony pentafluoride

“…Opening of the four-membered ring is likely to occur in intermediate cation Q which is thus converted into diarylmethyl cation R; addition of fluoride ion to the latter and subsequent fluorination yields perfluoro(2-propyldiphenylmethane) (XXXII). Hydrolysis of perfluoro(2-propyldiphenylmethyl) cation (XXXIII) generated from XXXII leads to compound XXVI [7]. Presumably, fluorene derivatives are formed as a result of cyclization of intermediate diarylmethane XXXII.…”

“…Cation D can also take up fluoride ion to form styrene E. Addition of HF to E leads to diarylmethane F, and fluorination of E leads to perfluoro(2-ethyldiphenylmethane) (XXI). As shown in [7], the reaction of XXI with SbF 5 generates perfluoro-(2-ethyldiphenylmethyl) cation (XXII), and hydrolysis of XXII yields perfluorinated 2-ethylbenzophenone X. Scheme 3 illustrates possible pathways of transformation of diarylmethanes F and XXI into reaction products.…”