Natural and synthetic chromenes, fused chromenes, and versatility of dihydrobenzo[h]chromenes in organic synthesis.

Cobalt(III)–carbene radicals, generated through metalloradical activation of salicyl N-tosylhydrazones by cobalt(II) complexes of porphyrins, readily undergo radical addition to terminal alkynes to produce salicyl–vinyl radical intermediates. Subsequent hydrogen atom transfer (HAT) from the hydroxy group of the salicyl moiety to the vinyl radical leads to the formation of 2H-chromenes. The Co(II)-catalyzed process can tolerate various substitution patterns and produces the corresponding 2H-chromene products in good isolated yields. EPR spectroscopy and radical-trapping experiments with TEMPO are in agreement with the proposed radical mechanism. DFT calculations reveal the formation of the salicyl–vinyl radical intermediate by a metalloradical-mediated process. Unexpectedly, subsequent HAT from the hydroxy moiety to the vinyl radical leads to formation of an o-quinone methide intermediate, which dissociates spontaneously from the cobalt center and easily undergoes an endocyclic, sigmatropic ring-closing re...

Metalloradical Approach to 2H-Chromenes

Syntheses of chromenes and chromanes via o-quinone methide intermediates

An iron-catalyzed intramolecular alkyne−aldehyde metathesis strategy of the alkynyl ether of salicylaldehyde derivatives has been developed which works under mild reaction conditions to produce the functionalized 2H-chromene derivatives. This protocol is compatible toward a wide range of functional groups, such as methoxy, fluoro, chloro, bromo, and phenyl groups. This method provides an atom-economical and environmentally friendly approach for the synthesis of a series of substituted 2H-chromenes.

Iron-Catalyzed Synthesis of Functionalized 2H-Chromenes via Intramolecular Alkyne−Carbonyl Metathesis

Activity-guided isolation of antiplasmodial dihydrochalcones and flavanones from Piper hostmannianum var. berbicense

Piper crassinervium, P aduncum, P hostmannianum, and P gaudichaudianum contain the new benzoic acid derivatives crassinervic acid (1), aduncumene (8), hostmaniane (18), and gaudichaudianic acid (20), respectively, as major secondary metabolites Additionally, 19 known compounds such as benzoic acids, chromenes, and flavonoids were isolated and identified The antifungal activity of these compounds was evaluated by bioautographic TLC assay against Cladosporium cladosporioides and C sphaerospermum

Diego Campos C. Casanova

Papers

Benzoic Acid Derivatives from Piper Species and Their Fungitoxic Activity against Cladosporium cladosporioides and C. sphaerospermum