Naturally occurring benzo furans

The commonest five-membered heteroaromatic compounds containing one heteroatom are pyrrole (30), furan (31) and thiophene (32). Their substituted derivatives and the substituted derivatives of the corresponding benzo analogues [indole (33), benzofuran (34) and benzothiophene (35)] are widespread naturally-occurring compounds. 

Numerous examples of natural products with the benzo[ ]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. 

In the total synthesis of naturally occurring frondosin B, the palladium-catalyzed coupling reaction of C-3 stannylated benzo[. ]furan 94 with the vinyl triflate 95 was employed as a key step to build up the framework of the final target, as depicted in Equation (89) <2001JA1878>. 

Those naturally occurring compounds containing benzo[fc]furan, dihydrobenzo[fc]furan or dihydrobenzo[c]furan skeletons, whose biologicd activities have been assessed are... 

As depicted below, a procedure for the iodocyclization of acetoxy-containing 2-(l-alkynyl)anisole and subsequent direct palladium-catalyzed earbonylatiori/lactonization was reported as an efficient entry to naturally occurring eoumestan and coumestrol <05IOC9985>. A novel Pd(II)-mediated cascade carbonylative annulation of substituted o-hydroxyphenylacetylenes to give benzo[fo]furan-3-carboxylie adds was achieved in a one-pot reaction <050L2707>. 

References on those naturally occurring compounds containing benzo f>Jfuran or dihydrobenzo[ )]furan skeletons whose biological activities were assessed are <04H(63)879> and <04P3021>. 

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