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 Chang Guo Basudev Sahoo Constantin G. Daniliuc Frank Glorius 10.1021/ja510737n.s001 https://acs.figshare.com/articles/journal_contribution/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/2224543 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% <i>ee</i>). 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. 2014-12-17 00:00:00 ee Diazepine Annulation enal vs yield enantioselective diazepine annulation access functionalized pyrazoles reactivity role Carbene PyrazolesA regio Synthesi enantioselectivitie Azoalkene carbene reaction pathway steric properties Catalyzed NHC catalyst substrate pyrazole derivatives homoenolate Enal azoalkene organocatalyst Switchable Formal