The photolysis of diazomethane in ethereal solution was studied by Meerwein and co-workers in 1942 and is probably one of the first examples for the direct, yet unselective, functionalization reaction of unreactive C−H bonds. We have explored this approach in the C−H and N−H functionalization and cyclopropanation reaction of N-heterocycles and could demonstrate the applicability of this method in 51 examples. Following this strategy, the concentration of the diazoalkane reaction partner can be minimized to reduce unwanted side reactions and to now conduct photochemical carbene transfer reactions under stoichiometric reaction conditions. Herein, we describe a protocol that takes advantage of the in situ generation of donor–acceptor diazoalkanes by Bamford–Stevens reaction. One of the major limitations lies within the rapidly occurring side reaction of the carbene intermediate with remaining diazoalkane molecules that result in the use of an excess of the reaction partner and thus impacts on the reaction efficiency. The photolysis of diazoalkanes is a timely strategy to conduct carbene-transfer reactions under mild and metal-free reaction conditions, and has developed as an important alternative to conventional metal-catalyzed carbene-transfer reactions.
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March 2023
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