RESUMEN
A short synthetic route to the trimethyl ether of brazilin was developed in 6 steps from 7-methoxychromene with 78% overall yield. Regioselective installation of a formyl group onto 7-methoxychromene followed by reduction and acetylation afforded allylic acetate. Palladium-catalyzed allylic coupling of allylic acetate with arylboronic acid provided direct access to 3-benzylchromene which was converted to the target molecule upon ensuing dihydroxylation and acid-catalyzed cyclization in a highly concise manner.
Asunto(s)
Acetatos/química , Compuestos Alílicos/química , Benzopiranos/síntesis química , Paladio/química , Benzopiranos/química , Catálisis , Técnicas de Química Sintética , CiclizaciónRESUMEN
Described herein is a highly efficient total synthesis of brazilin from commercially available starting materials in 9 steps with 70% overall yield. Mitsunobu coupling followed by In(III)-catalyzed alkyne-aldehyde metathesis allowed for rapid construction of brazilin core skeleton in quantitative yield. Subsequent modulation of oxidation levels and acid-catalyzed cyclization led to the trimethyl ether of brazilin. Asymmetric dihydroxylation of the key intermediate was also demonstrated, which would permit asymmetric access to (+)-brazilin.