Combining palladium and ammonium halide catalysts for Morita-Baylis-Hillman carbonates of methyl vinyl ketone: from 1,4-carbodipoles to ion pairs.
Chem Sci
; 12(34): 11399-11405, 2021 Sep 01.
Article
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| MEDLINE
| ID: mdl-34667548
ABSTRACT
Here we report that Morita-Baylis-Hillman carbonates from diverse aldehydes and methyl vinyl ketones can be directly utilised as palladium-trimethylenemethane 1,4-carbodipole-type precursors, and both reactivity and enantioselectivity are finely regulated by adding a chiral ammonium halide as the ion-pair catalyst. The newly assembled intermediates, proposed to contain an electronically neutral π-allylpalladium halide complex and a reactive compact ion pair, efficiently undergo asymmetric [4 + 2] annulations with diverse activated alkenes or isatins, generally with high regio-, diastereo- and enantio-selectivity, and even switchable regiodivergent or diastereodivergent annulations can be well realised by tuning the substrate or catalyst assemblies. An array of control experiments, including UV/Vis absorption study and density functional theory calculations, are conducted to rationalise this new double activation mode combining a palladium complex and an ammonium halide as an ion-pair catalyst.
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01-internacional
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MEDLINE
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En
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Chem Sci
Año:
2021
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Article