Reaction of glyoxal at the ortho position of phenols. Synthesis of 5a,10b-dihydrobenzofuro[2,3-b]benzofurans and 2-(3-benzofuranyl)phenols

The acid-catalyzed reaction of glyoxal at the ortho position of phenols has been shown to yield, as initial products, substituted 5a,10b-dihydrobenzofuro[2,3-b]benzofurans, such structures being indicated by the nuclear magnetic resonance spectra, and confirmed in several cases by synthesis via an unambiguous route. At higher temperatures in acidic media, and in the absence of glyoxal, these initial products were converted into the corresponding 2-(3-benzofuranyl)phenols. When glyoxal was present in acidic media, the 2-(3-benzofuranyl)phenols reacted further to give unidentified products of appreciably higher molecular weight.