Photocatalytic Oxo-Amination of Aryl Cyclopropanes through an Unusual SN2-Like Ring-Opening Pathway: Won >99% ee.
J Org Chem
; 87(21): 13627-13642, 2022 11 04.
Article
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| MEDLINE
| ID: mdl-36174109
ABSTRACT
One-pot oxo-amination of unactivated cyclopropanes with safe, green dioxygen as an oxidant and low-cost amines as nitrogen sources has generated interest since this can directly result in uniform ß-located difunctional units. Formation of the three-electron cation radical followed by the nucleophilic attack of amines to open the strained ring of cyclopropanes catalyzed by classic noble-complex photocatalysts was a promising strategy. However, this ring-opening pathway could not maintain the entire second-order nucleophilic substitution (SN2) conversion, which generally led to unsatisfactory enantioselectivity (enantiomeric excess (ee) value â¼60%). Here, we demonstrate that for such a one-step oxo-amination of cyclopropanes with benign dioxygen and pyrazoles, a highly uniform inversion of configuration could be first accomplished through a TiO2 photocatalyst. This strategy features low-cost, semiheterogeneous photocatalysis and environmentally friendly reaction conditions, without using any sacrificial reagent or additive. Importantly, our protocol not only provides a relatively broad substrate scope tolerant to a certain range of substituted cyclopropanes and pyrazoles, resulting in various ß-amino ketone products (â¼50 examples) with excellent conversions and yields, but also retains excellent enantioselectivity (ee value â¼99%). A concerted SN2 ring opening raised from an oxetane cation intermediate rather than a conventional three-electron cation radical prior to attaching to dioxygen was proposed.
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Bases de datos:
MEDLINE
Asunto principal:
Ciclopropanos
/
Aminas
Idioma:
En
Revista:
J Org Chem
Año:
2022
Tipo del documento:
Article