Diarylethenes unsymmetrical

Scheme 30 Synthesis of an unsymmetrical diarylethene using a multistep microflow system [66]...

The reaction scope is further enlarged to unsymmetrically disubstituted derivatives. Using one mole equivalent of two different aryllithium precursors at a time in a sequence of four micromixers and microtube reactors (MRi ), it was possible to obtain an unsymmetrically disubstituted final diarylethene. The yield was determined after solvent evaporation and sample purification on the column. 

The synthesis of diarylethenes from hetaryl bromides and octafluoro-cyclopentene using a microflow system allows the preparation of various symmetrical and unsymmetrical diarylperfluorocyclopentenes in 47-87% yields at 0°C (07CC2947). 

Using a stainless-steel microreactor, Ushiogi et al. (2007) reported a microflow system capable of synthesizing unsymmetrical diarylethenes, a process that is notoriously difficult to achieve in conventional batch systems. As Scheme 62 illustrates, diarylethenes are of synthetic interest due to their ability to change color via a reversible switching between two distinct isomers, which occurs as a result of light absorption. 

Scheme 63 Schematic detailing the general protocol employed for the continuous flow synthesis of (a) symmetrical and (b) unsymmetrical diarylethenes.

Figure 10.4 Synthesis of unsymmetrical diarylethenes in a microflow system...

The successful synthesis of unsymmetrical diarylethenes using two different aryl bromides in a single flow speaks well for the potential of microfiow systems in making new functional materials, which would be otherwise difficult to synthesize in a conventional manner. Acceptable productivity from the viewpoint of industrial production of functional materials can be attained using microtube reactors with a relatively large inner diameter (800/rm) without numbering-up. 

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