SYNTHETIC FUROCOUMARINS .9. A NEW SYNTHETIC ROUTE TO PSORALEN

Practical syntheses of psoralen (IVb) and 3-methylpsoralen (IVc) from β-resorcylaldehyde are described. Bromination of ethyl (2-formyl-5-methoxyphenoxy)acetate gave the 4-bromo derivative la, which was saponified and simultaneously cyclized and decarboxylated to 5-bromo-6-methoxybenzofuran (IIa). Lithium-bromine interchange and then formylation and demethylation gave 5-formyl-6-hydroxybenzofuran (III), which was condensed with diethyl malonate to furnish psoralen after hydrolysis and decarboxylation of the Knoevenagel product IVa. Condensation of III with propionic anhydride furnished 3-methylpsoralen (IVc) directly. © 1969, American Chemical Society. All rights reserved.