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