Partially fluorinated heterocyclic compounds. Part 27. The synthesis of 4,5,6,7-tetrafluorobenzo[c]thiophene and 4,5,6,7,8,9-hexafluoronaphtho-[1,2-c]thiophene; some chemistry and electrochemistry

Abstract

2,3,4,5,6-Pentafluorobenzyl methyl sulphoxide (6) is readily converted by butyl-lithium into 4,5,6,7-tetrafluorobenzo[c]thiophene (8) and 1,3,4,5,6,7,8-heptafluoro-2-naphthylmethyl methyl sulphoxide (9) in a similar manner gives a very low yield of 4,5,6,7,8,9-hexafluoronaphtho[1,2-c]thiophene (11) accompanied by the 7- and 8-butylated derivatives (12) and (13) respectively, and also 1,3,4,5,6,7,8-heptafluoronaphthalene-2-carbaldehyde (10). Compound (8) undergoes Diels–Alder addition reactions followed by sulphur elimination with dimethyl acetylenedicarboxylate and tetrafluorobenzyne to give the naphthalene and anthracene derivatives (14) and (15) respectively. With lithium propane-2-thiolate, compound (8) gives the 5-propan-2-ylthio and 5,6-bispropan-2-ylthio derivatives (16) and (17) respectively. Compound (8) is polymerisedby SbF₅–HF to poly(1,3-dihydro-4,5,6,7-tetrafluorobenzo[c]-thiophene)(20). The electrochemical anodic oxidation of (8) has been studied extensively: polymer (20) is produced accompanied by a deep red material readily soluble in chloroform, which is not poly(4,5,6,7-tetrafluorobenzo[c]thiophene)(24).