Transition metal catalysts have inevitably been used for C(
sp2)-C(
sp2) bond forming reactions of aryl halides with
sp2-carbon nucleophiles. On the other hand, we have recently developed such a kind of reactions with no aid of transition metal catalysis, utilizing single electron transfer (SET) mechanism. Here, a single electron acts as a catalyst to promote the reaction of aryl halides (Ar-X) with arenes, styrenes or aryl Grignard reagents (ArMgBr) to give biaryls, stilbenes or biaryls, respectively. The common intermediates are anion radicals ([Ar-X]
•−) of aryl halides and those ([Ar-R]
•−) of coupling products. [Ar-X]
•−, generated through SET from a base or ArMgBr to Ar-X, reacts directly with ArMgBr, whereas less reactive arenes and styrenes react with Ar
•, generated by decomposition of [Ar-X]
•−. All the reactions include, in the last step, SET from [Ar-R]
•− to Ar-X to give Ar-R and regenerate [Ar-X]
•−.
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