Guo, Chang Sahoo, Basudev Daniliuc, Constantin G. Glorius, Frank 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 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. 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 2014-12-17
    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
10.1021/ja510737n.s001