(64d) Synthesis of Photochromic Diarylethenes Using a Microflow System

Diarylethene derivatives have received significant research interest from both academia and industry, because some of them exhibit remarkable changing of color by reversible switching of two distinct isomers (photochromism). Such diarylethenes have been synthesized by the reaction of aryllithium compounds with octafluorocyclopentene in a batch reactor at low temperatures such as -78 °C in order to avoid undesirable side reactions. The requirement of such low temperatures, however, causes severe limitations in the industrial production. Herein we report that the synthesis of diarylethenes can be accomplished at 0 °C by the use of microflow system by virtue of effective temperature control and residence time control. The first step of the synthesis of diarylethenes is the halogen-lithium exchange reaction of an aryl bromide with butyllithium. In the next step, the aryllithium compound is allowed to react with octafluorocyclopentene. Both reactions should be carried out at low temperatures. Thus, we constructed a microflow system consisting of T-shaped micromixers and microtube reactors. Various diarylethenes were successfully synthesized using the microflow system. The effective temperature control of the microflow system, which minimizes local deviation of the temperature and suppresses the decomposition of the reactive intermediates, seems to be responsible for the success of the reaction at much higher temperature.