Abstract
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.
Highlights
Existing synthetic routes for accessing dibenzofuran core have intrinsic regioselectivity, limiting the substitution patterns available in heteropolycyclic arene products
Dibenzofuran-containing heterocycle constitutes an important structural motif in many natural products, pharmaceutically intermediates, and functional materials[1,2,3,4,5,6,7]. These flanked-arenes furans are shown to have appealing characteristics, such as antibiotics, antimalarial, antiallergy, antiinflammatory, and anticancer activities[8,9,10,11]. They express their versatility in photoelectronic materials, especially in phosphorescent organic light-emitting diodes (PhOLEDs)[12,13,14], and chemical probes in biological process investigations[15,16,17]
Representative synthetic strategies in this context are intramolecular ring closure pathways for achieving targeted dibenzofurans, either from a starting material of diaryl ether or ortho-arylphenol, via an aromatic carbon–carbon or carbon–oxygen bond-forming process, respectively (Fig. 1)
Summary
Existing synthetic routes for accessing dibenzofuran core have intrinsic regioselectivity, limiting the substitution patterns available in heteropolycyclic arene products. We report a cascade reaction between propargylic amines and imidazolium methylides (Fig. 1d). Room temperature conditions did not allow the reaction to proceed (entry 24).
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