Synthesis, properties and conformational studies of anti-8-fluoro-16-methyl-[22]metacyclophane and anti-8-fluoro-16-methyl[22]metacyclophane-1,9-diene

Abstract

The protons of the anti and syn isomers, 5b and 6b, of 9-fluoro-18-methyldithia[32]metacyclophane have been assigned by 1D and COSY 1H NMR spectral data. A Stevens rearrangement-Hofmann elimination sequence carried out with a mixture of 5b and 6b led only to the isolation of anti isomers of 8-fluoro-16-methyl[22]metacyclophane-1,9-diene 1f and 8-fluoro-16-methyl-10-methylsulfanyl[22]metacyclophan-1-ene 11. The photochemical and thermal decomposition of 1f resulted in the formation of mainly pyrene and methylpyrenes. Dihydropyrene 2f is probably the initial intermediate and the products are believed to be formed from subsequent carbocation formation and methyl shifts. The reduction of compound 11 led to the isolation of pyrene and anti cyclophane 17c. The cyclophanene 16c is believed to be the intermediate which undergoes 'disproportionation reactions' to give cyclophane 17c and cyclophanediene 1f (and thus pyrene). The protons in the bridges of 17c could be assigned on the basis of NOE and decoupling experiments. Downfield shifts of the methyl signals are observed in passing from 17c to 11 and 1f, and going from 17a to 17c, 16a to 11 and 1b to 1f, respectively. This is attributed to a change in molecular geometry resulting from the 'sliding' of the anti, stepped benzene rings.