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N-Heterocyclic Carbene Catalyzed Switchable Reactions of Enals with Azoalkenes: Formal [4 + 3] and [4 + 1] Annulations for the Synthesis of 1,2-Diazepines and Pyrazoles

2014; American Chemical Society; Volume: 136; Issue: 50 Linguagem: Inglês

10.1021/ja510737n

1943-2984

Chang Guo, Basudev Sahoo, Constantin G. Daniliuc, Frank Glorius,

Catalytic C–H Functionalization Methods

A regio- and enantioselective formal [4 + 3] annulation reaction between enals and in situ formed azoalkenes has been achieved. A diverse set of 1,2-diazepine derivatives were synthesized in good yields with excellent enantioselectivities (often 99% ee). Alternatively, modifying the standard NHC catalyst switched the reactivity toward a formal [4 + 1] annulation to afford functionalized pyrazoles. The electronic and steric properties of the N-heterocyclic carbene organocatalyst play a vital role in controlling the reaction pathway (homoenolate vs acyl-anion reactivity of enal), allowing selective access to diverse 1,2-diazepine and pyrazole derivatives from identical substrates.