Beilstein J. Org. Chem.2020,16, 2920–2928, doi:10.3762/bjoc.16.241
-bromoacetaldehyde acetal by using aluminum(III) chloride as a Lewis acid catalyst through [1 + 2 + 2] annulation. This new versatile methodology provides a wide scope for the synthesis of different functional N-(hetero)aryl-4,5-unsubstituted pyrrole scaffolds, which can be further derived to access multisubstituted
pyrrole-3-carboxamides. In the presence of 1.2 equiv of KI, a polysubstituted pyrazolo[3,4-b]pyridine derivative was also successfully synthesized.
Keywords: acid catalyst; [1 + 2 + 2] annulation; KI; pyrazolo[3,4-b]pyridine; pyrroles; Introduction
Among nitrogen-containing heterocycles, pyrroles have
the 1,4-dicarbonyl compounds [34][35], γ-carbonyl tert-butyl peroxides [36], and dihydrofurans [37] have also been reported to construct the pyrrole skeletons through this type of annulation; and (iii) [1 + 2 + 2] annulation, in which (hetero)arylamines are reacted with two different molecules, and
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Graphical Abstract
Figure 1:
Representative biologically active N-(hetero)aryl-4,5-unsubstituted pyrrole scaffolds.