title: 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.
abstract: 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.
authors.affiliation: Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster , Corrensstraße 40, 48149 Münster, Germany.
authors.forename: Chang
authors.initials: C
authors.lastname: Guo
authors.forename: Basudev
authors.initials: B
authors.lastname: Sahoo
authors.forename: Constantin G
authors.initials: CG
authors.lastname: Daniliuc
authors.forename: Frank
authors.initials: F
authors.lastname: Glorius