OLIGOMERIC POLYPARATETRAFLUOROPHENYLENE VINYLENES - A NEW SYNTHESIS BASED ON THE NUCLEOPHILIC-SUBSTITUTION OF THE PARA FLUORINE DURING THE REACTION OF (E)-2-(PENTAFLUOROPHENYL)ETHENYL LITHIUM WITH HEXAFLUOROBENZENE

(E)-2-(Pentafluorophenyl)ethenyl bromide (3) has been prepared by three routes: (i) bromination of 2,3,4,5,6-pentafluorocinnamic acid (5) gave 1,2-dibromo-2-(pentafluorophenyl)propionic acid (6) which was converted into 1,1,2-tribromo-2-(pentafluorophenyl)ethane (7) via the Hunsdiecker reaction; (3) was formed by the debromination of (7) with zinc; (ii) the reaction of (6) with red mercuric oxide and bromine gave (3) and (7); (iii) hydroboration of 2,3,4,5,6-pentafluorophenylethyne (8) with catecholborane followed by hydrolysis of the intermediate gave (E)-2-(pentafluorophenyl)ethenyl boronic acid (9) which on treatment with alkali and bromine gave (3). The boronic acid (9) was converted into (E)-2-(pentafluorophenyl)ethenyl iodide (4) with alkali and iodine. The bromo compound (3) was inactive towards magnesium and n-butyllithium brought about fluorine replacement to give (10). The iodo compound (4) formed the lithium derivative (11) with n-butyllithium which reacted in C6F6 to give (E)-decafluorostilbene (12) and oligomeric compounds, (13), (14) and (15); in the absence of C6F6, oligomer (16) was formed which had a conductivity < 10-10 S cm-1. © 1990.