Abstract
The asymmetric annulation of a range of α,β-unsaturated acyl ammonium intermediates, formed from isothiourea HBTM 2.1 and anhydrides with either 1,3-dicarbonyls, β-ketoesters or azaaryl ketones gives either functionalised esters (upon ring opening), dihydropyranones or dihydropyridones in good yields (up to 93%) and high enantioselectivity (up to 97% ee).
Highlights
Introduction and backgroundAsymmetric organocatalysis has developed tremendously as a synthetic strategy within the last decade and a range of methodologies and catalysts have emerged that provide functionalised products with high levels of stereocontrol.1 Ideally a given organocatalyst architecture should be able to participate in a range of reaction processes and display diverse modes of reactivity, while showing good catalytic efficiency and delivering products with high levels of enantioselectivity
The asymmetric annulation of a range of a,b-unsaturated acyl ammonium intermediates, formed from isothiourea HBTM 2.1 and anhydrides with either 1,3-dicarbonyls, b-ketoesters or azaaryl ketones gives either functionalised esters, dihydropyranones or dihydropyridones in good yields and high enantioselectivity
Given the recognised difficulties in accessing a wide variety of ynals and enals for such NHC-catalysed approaches and limitations associated with the scope and generality of such processes,21 we envisaged a direct strategy to generate an a,bunsaturated acyl ammonium species from readily available a,bunsaturated carboxylic acids or their anhydrides
Summary
Anhydrides as a,b-unsaturated acyl ammonium precursors: isothiourea-promoted catalytic asymmetric annulation processes†. The asymmetric annulation of a range of a,b-unsaturated acyl ammonium intermediates, formed from isothiourea HBTM 2.1 and anhydrides with either 1,3-dicarbonyls, b-ketoesters or azaaryl ketones gives either functionalised esters (upon ring opening), dihydropyranones or dihydropyridones in good yields (up to 93%) and high enantioselectivity (up to 97% ee)
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