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.
J Am Chem Soc
; 136(50): 17402-5, 2014 Dec 17.
Article
em En
| MEDLINE
| ID: mdl-25418586
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.
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MEDLINE
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En
Ano de publicação:
2014
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Article