A novel and efficient strategy has been developed for the synthesis of 3-triazolylcoumarins in a one-pot, copper-catalyzed multicomponent reaction involving a cascade reaction of salicylaldehydes, ethyl 2-azidoacetate, and arylacetylenes.

Existing synthetic routes for accessing dibenzofuran core have intrinsic regioselectivity, limiting the substitution patterns available in heteropolycyclic arene products. Here we report a double 1,4-conjugate addition/intramolecular annulation cascade reaction between propargylamines and two equivalents of imidazolium methylides that allows efficient access of structurally versatile dibenzofurans. This transition metal-free protocol proceeds smoothly under bench-top air atmosphere and offers easy manipulation of substituents on the dibenzofuran core, and also provides good-to-excellent product yields with good functional group tolerance, particularly the –Br and –Cl groups which are often incompatible with existing metal-catalyzed C–C and/or C–O bond ring-forming processes. It is worth noting that ladder-type π-systems with all-arene quarternary carbon structure can be straightforwardly generated upon simple late-stage functionalization.

A novel and versatile approach to construct 12-phenacyl-11H-benzo­[b]­xanthene-6,11­(12H)-dione derivatives through copper-catalyzed cascade reaction of propargylamines with 2-hydroxy­naphthalene-1,4-diones has been developed. The procedure is proposed to go through a sequence of 1,4-conjugate addition, intramolecular nucleophilic addition/dehydration, and hydrolysis of alkyne followed by an enol–ketone tautomerization. The reaction provides a new and highly efficient method for the synthesis of 12-phenacyl-11H-benzo­[b]­xanthene-6,11­(12H)-diones by formation of three new bonds and one heterocycle from readily available starting materials in good to high yields (70–88%) with broad functional group compatibility in a single step.

A Rh­(III)-catalyzed cascade nucleophilic addition/intramolecular annulation of 2-diazo-1,3-diketones with 1,3-dicarbonyl compounds (e.g., 1,3-diketones and β-keto esters) is achieved to afford 6,7-dihydrobenzofuran-4­(5H)-ones in up to 91% yields. Notably, a wide range of substrates and functional groups were well-tolerated under the optimized reaction conditions to give desired products in moderate to excellent yields with release of N2 and H2O as byproducts. Moreover, the method described is scalable and adaptable to late-stage functionalization.

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.