Regioselective synthesis of 4,10-dihydro-3-hydroxy-3-methyl-1H,3H-pyrano[4,3-b][1]benzopyran-10-one, the basic skeleton in fulvic acid
Abstract
The first synthesis of 4,10-dihydro-3-hydroxy-3-methyl-1H,3H-pyrano[4,3-b][1]benzopyran-10-one, the basic skeleton in fulvic acid, was achieved by sequential cyclization, which involved hydrogenation of the boron complex of the dione (5) obtained by regioselective cyclization of the acetal (4) with HCl in tetrahydrofuran.