Clarification of the Reactivity of Octafluorocyclopentene toward Carbon Nucleophiles and Its Application to Functional Molecules

Hexafluorocyclopentene derivatives produced by the reaction of octafluorocyclopentene (OFCP) with nucleophiles are promising functional materials, such as diarylethene-type photochromic molecules, electrochromic molecules, turn-on/turn-off fluorescent switching molecules, and heat-resistant polymers. Although many reactions of OFCP with heteroatom nucleophiles, like alcohols, amines, and thiols, have been reported, the systematic reactivity with carbon nucleophiles has not yet been fully elucidated. Reactivity studies of OFCP with various carbon nucleophiles revealed that the reaction with Griganrd reagent efficiently produces monosubstituted products, whereas the reaction with organolithium reagents preferentially produces 1,2-disubstituted products. Reactions with excess amounts of stable carbanions, such as diethyl sodiomalonate and methylidenetriphenylphosphorane, were found to proceed in a unique addition-elimination/1,4-HF-elimination/addition-elimination sequence to produce the corresponding 1,3-disubstituted products in high yields. During these systematic studies, it was found that 1,2-bis(arylethynyl)-3,3,4,4,5,5-hexafluorocyclopentene, formed in the reaction of OFCP with arylethynyllithium, is available as a dual-state fluorescent molecule that fluoresces in solution as well as in solid state. Furthermore, the products obtained in the reaction with phosphonium ylides, namely merophosphinines and phosphinines, also proved to be promising functional dyes as analogues of merocyanine and cyanine dyes. These achievements demonstrate that the reaction of OFCP with nucleophiles is a useful synthetic approach for incorporating cyclic fluorinated alkene backbones into functional molecules.