Cascade Lactonization/Benzannulation of Propargylamines with Dimethyl 3-Oxoglutarate for Modular Assembly of Hydroxylated/Arene-Functionalized Benzo[c]chromen-6-ones

Abstract

A DBU-mediated cascade strategy of propargylamines with dimethyl 3-oxoglutarate for constructing a functionalized benzo­[c]­chromen-6-one core has been achieved. This cascade process presumably involves a sequence of 1,4-conjugate addition, followed by lactonization, alkyne–allene isomerization, enol–keto tautomerization, 6π-electrocyclization, and aromatization. This protocol features mild reaction conditions, simple operation, rich structural diversity, and good functional group tolerance. A photophysical survey reveals that the benzo­[c]­chromen-6-one products exhibit fluorescence properties and show potential for exploring fluorescent material applications.

Cascade Annulation Strategy for Expeditious Assembly of Hydroxybenzo[c]chromen-6-ones and Their Photophysical Property Studies

“…In 2020, a tandem 4-dimethylaminopyridine (DMAP)-catalyzed annulation reaction between propargylamines and acyl carbene surrogate for accessing furan-fused chromenes was reported (Scheme b­(ii)) . Later, lactonization/benzannulation of o -AQM (in situ generated from propargylamines) with dimethyl 3-oxoglutarate was described to achieve the functionalized benzo­[ c ]­chromen-6-one derivatives (Scheme b­(iii)) . Very recently, Liu established a Brønsted acid-catalyzed tandem 1,6-addition/double annulation protocol using o -hydroxyphenyl propargylic alcohols and nitrones to give densely functionalized chromeno­[3,2- d ]­isoxazoles (Scheme b­(iv)) .…”

“…13 Later, lactonization/benzannulation of o-AQM (in situ generated from propargylamines) with dimethyl 3-oxoglutarate was described to achieve the functionalized benzo [c]chromen-6-one derivatives (Scheme 1b(iii)). 14 Very recently, Liu established a Brønsted acid-catalyzed tandem 1,6-addition/double annulation protocol using o-hydroxyphenyl propargylic alcohols and nitrones to give densely functionalized chromeno [3,2-d]isoxazoles (Scheme 1b(iv)). 15 In continuing our interest of investigating chromene 16 and fused arene systems, 17 we sought to adopt the o-AQM chemistry in a new cascade reaction between alkylaminophenols and 1-(4-ethoxy-2,4-dioxobutyl)pyridin-1-ium bromide, for modular assembly of hydroxybenzo [c]chromen-6-one with rich diversity of substitution patterns.…”

Copper-Catalyzed Cascade Annulation of o-Hydroxyphenyl Propargylamines with Pyrazolin-5-ones to Access Pyrano[2,3-c]pyrazoles

“…Despite impressive innovations, these reactions were mainly limited to the chemistry of o -HPPAs with active methylene compounds for the synthesis of chromene and benzofuran derivatives (Scheme b). Kwong et al have recently developed several new cyclization of o -HPPAs with β-naphthol, pyridinium ylide, dimethyl 3-oxoglutarate water, dipyridinium methylide, and imidazolium methylides . However, the obtainable products were still limited to chromene and benzofuran derivatives (Scheme b).…”

Radical-Induced Cascade Annulation/Hydrocarbonylation for Construction of 2-Aryl-4H-chromen-4-ones

“…In addition, transition-metal-catalyzed annulations often require the use of highly toxic carbon monoxide or expensive palladium catalyst and ligand at high temperatures. Inspired by our pioneering results, in which multireactive propargylamines displayed unique feature of cyclization, and in continuation of our interest in developing new synthetic protocols to build valuable heterocyclic frameworks [ 58 , 59 , 60 , 61 , 62 , 63 , 64 ], we herein disclose a cascade annulation of propargylamines for the synthesis of 2-aryl-4 H -chromen-4-ones under green and operationally simple metal- and solvent-free conditions, which is unprecedented in previous works ( Scheme 1 g). This cascade process presumably involves a sequence of radical-induced C-N cleavage, followed by C-O coupling, intramolecular 6- endo-dig annulation, thermal hemolytic cleavage, and oxidative hydrocarbonylation.…”