4-, 5-, 6-, and 7-Hydroxybenzofuran: a unified strategy for a two-step synthesis of versatile benzofuranic building blocks

Abstract

Over several decades, many different strategies have been reported to prepare 4-, 5-, 6-, and 7hydroxybenzofuran (HBF), which are very important synthetic intermediates. Interested in addition of their 2lithiated O-protected derivatives to transient 1-pyrroline as a straightforward way to nicotinoids, we have developed a unique two-step procedure to obtain 4-, 5-, 6-, and 7-HBF from 2,6-, 2,5-, 2-4-and 2,3dihydroxyacetophenone, respectively, by conversion into 4-, 5-, 6-and 7-hydroxybenzofuranone and successive reduction of these latter with lithium borohydride. On the basis of the overall yields, the number of steps and the availability of the starting materials, such a synthetic strategy can be advantageously compared with the literature methods, here briefly reviewed, developed to synthesize the four HBFs.