Photoinduced [3+2] Cycloaddition of Carbenes and Nitriles

Photoinduced [3+2] Cycloaddition of Carbenes and Nitriles

Author: ChemistryViews

Oxazole derivatives are often found in pharmaceutically active compounds. New methods for their synthesis are, thus, useful—for example, in drug development. Ideally, such methods require few steps, are atom-economic, have a broad substrate scope, and can be scaled up successfully. Photoinduced methods can be interesting in this context.

Debabrata Maiti, Indian Institute of Technology Bombay, Mumbai, India, and colleagues have developed a protocol for the synthesis of pharmaceutically useful oxazole derivatives via a photoinduced [3+2] cycloaddition of carbenes and nitriles (general product structure pictured above). The team started from α-carbonyl diazo compounds, which were reacted with nitriles in dichloroethane (DCE) under blue LED light over 24 h.



The desired oxazoles were obtained in moderate to high yields, with a wide spectrum of products. The reaction does not require metal catalysts and can also be used in a flow chemistry approach. The team proposes a mechanism (pictured above) that involves the formation of a carbene from the α-carbonyl diazo compound under light irradiation. The carbene can then be trapped by the nitrile to form a nitrogen ylide intermediate. Finally, an intramolecular [3+2] cycloaddition gives the desired oxazole product.


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