Naturally occurring dibenzofurans

Naturally occurring oxaarenes based on polycyclic pyrans encompass a plethora of structures including the plant polyphenols such as anthocyanins and a-tocopherol (vitamin E). Halogenated dibenzo-p-dioxins and dibenzofurans are formed both as by-products during the manufacture of chlorophenols, and from the incineration of organic matter in the presence of inorganic halides. 

The cellular slime mold Dictyostelium purpureum K1001 contains AB0022A (2255), a novel antibacterial dibenzofuran, the structure of which was confirmed by total synthesis (2038). The lichen Lecanora cinereocarnea has yielded several new dibenzofurans, including three chlorinated analogues (2256-2258) (2039), and Lecanora iseana contains 2259 and 2260 (2040). The first naturally occurring polybrominated dibenzofuran, corallinafuran (2261), is present in a crustose coralline red alga that also contains corallinaether (1913) cited earlier (1769). 

As many naturally occurring dibenzofurans possess a 3-hydroxy substituent, the reactions of trans-2-(2-methoxyvinyl)benzofuran 8 were studied (68TL4589 70AJC2119). The reaction with DMAD yielded three products, none of which had the expected structure 9. The major product was... 

Carvalho CF, Sargent MV (1984a) Naturally occurring dibenzofurans. Part 4. Synthesis of dibenzofurandiols by annellation of benzofurans. J Chem Soc Perkin Trans 1 1605-1612... 

Giles RGF, Sargent MV (1986) Naturally occurring dibenzofurans. X. A new synthesis of di-O-meth-ylstrepsilin. Aust J Chem 39 2177-2181... 

Carvalho CF, Sargent MV (1984) Naturally Occurring Dibenzofurans. Part 5. Synthesis of Melacarpic Acid. J Chem Soc Perkin I 1613... 

Numerous examples of natural products with the benzo[6]furan nucleus have been identified. It occurs under many guises dibenzofurans, /3-coumaranones, a-pyranobenzo[6]furans, y-pyranobenzo[6]furans, and the spiro-2,3-dihydrobenzofurans such as griseofulvin. Many of the natural benzo[6]furans have physiological, pharmacological and toxic properties and as a result an active interest exists in their chemical synthesis. 

---