POLYFLUORO-COMPOUNDS BASED ON THE CYCLOHEPTANE RING SYSTEM. PART 5. OCTAFLUOROCYCLOHEPTA-1,3,5-TRIENE AND HEXAFLUOROTROPONE

Article abstract of DOI:10.1016/S0022-1139(00)81295-6

Decafluorocyclohepta-1,3-diene underwent reductive addition-elimination with sodium borohydride to give mainly 1H-nonafluorocyclohepta-1,3-diene, together with minor products, the 1H,4H-octafluoro-analogue and, most significantly, 5H-nonafluorocyclohepta-1,3-diene.Decafluorocyclohepta-1,4-diene, together with some 6H-nonafluorocyclohepta-1,4-diene and a trace of the 5H-1,3-diene.These last two dienes were important products, having hydrogen on allylic carbons.They could be dehydrofluorinated, either by bubbling through molten potassium hydroxide or, better, with powdered alkali in an inert medium.Unless special precautions were taken, such reactions yielded hexafluorotropone.With care however the primary product, octafluorocyclohepta-1,3,5-triene, could be isolated, but it was hydrolysewd rapidly, even by water, to give the tropone.Isomerizations and pyrolytic dehydrofluorinations of the major reduction products were carried out, but none yielded the triene or the tropone.It seemed that the triene was probably formed but decomposed to give perfluoroarenes.An interesting defluorination pathway was also operating, to give pentafluorobenzene. 2H-Nonafluorocyclohepta-1,3-diene was an isomerization product.Hexafluorotropone reacted with sodium methoxide in methanol to give 3,6-dimethoxytetrafluorotropone.