A biomimetic approach to dihydrobenzofuran synthesis

A method for an acid-catalyzed construction of dihydrobenzofuran heterocycl es (14) from 2-(2 ' -hydroxyethyl)quinone precursors 10 is presented. The p utative oxonium. ion intermediate 17 formed by an intramolecular hydroxyl c yclization followed by dehydration is reduced in situ by an added dihydroqu inone source. Good to excellent yields of cyclized products are realized in all cases except for highly electron deficient systems, and these suffer r eduction prior to oxonium ion formation. All products are monomeric and der ived from a two-electron transfer except for 10g, which affords the dimeric dihydrobenzofuran. The amount of cyclization or reduction product is gover ned by the HOMO/LUMO gap between the quinone substrate and the dihydroquino ne additive, and the product distribution can be adjusted by modifying the electronic properties of the added reducing agent.