Magnetically recoverable silica catalysed solvent-free domino Knoevenagel-hetero-Diels–Alder reaction to access divergent chromenones

Abstract

A silica catalyzed solvent-free three-component domino Knoevenagel-hetero-Diels–Alder (DKHDA) reaction between 1,3-dicarbonyl, aldehydes/ketones, and alkenes/alkynes leading to chromenones, dihydrochromenones and spirochromenones has been described.

Recent Applications of the Diels–Alder Reaction in the Synthesis of Natural Products (2017–2020)

“…The chromene core is a widespread motif in both natural products and important pharmaceuticals with anthelmintic, anticancer, molluscicide and anti-HIV-1 activities. 89…”

“…By reacting 1,3-cycloalkanediones 280 with benzaldehyde derivatives 281 and terminal alkynes/alkenes 282 (Scheme 66) in the presence of magnetically recoverable silica, an initial Knoevenagel reaction takes place to furnish exoenone 283 thus setting the stage for the [4+2]heterocycloaddition. The chromene core is a wide-spread motif in both natural products and important pharmaceuticals with anthelmintic, anticancer, molluscicide and anti-HIV-1 activities 89.…”

A Tandem Aldol Condensation/Diels‐Alder Sequence of Reactions for One‐Pot Synthesis of a New Series of Polysubstituted‐Decalines

“…, [13] leading to efficient synthesis of pharmaceuticals, [14] natural products, [15] and other molecules of choice. [16] Illustrative multicomponent syntheses involving a DA reaction as the key step include a tandem sequential double DA/ Nazarov reaction in an unsymmetrically substituted diynone to yield a tricyclic scaffolds (such as taiwaniaquinol D), [17] the synthesis of chromenoquinolones via an imine formation/aza-DA/aromatization tandem process, [18] a sequence of DA and intramolecular [3 + 2] cycloadditions of dienylcyclopropane 1,1diesters for rapid construction of fused carbocyclic structures (such as brussonol), [19] a domino Knoevenagel-hetero-DA reaction to access various chromenones, [20] a twelve-step synthetic rout, having the DA reaction as the key step, to the structural core of aflavinines, [21] synthesis of ring-fused 2-cyclopentenone moieties, found in the skeleton of many natural and bioactive compounds like helenalin, via a gold-catalyzed cycloisomerization/hetero-DA/ring-opening sequence of tandem reactions of enynyl acetates, [22] an organocatalyzed sequence of oxa-Michael/Michael/Michael/aldol condensation reactions followed by an intramolecular DA cycloaddition leading to asymmetric synthesis of functionalized tricycles, [23] asymmetric multicomponent synthesis of bioactive alkaloid-type polycycles through catalytic aza-DA reaction of indoles having oxetane as the directing group, [24] and a tandem aldol condensation-DAaromatization sequence of reactions to access 2-tetralones (like serteraline) [25] [Figure 1].…”