Benzo furans 2- phenol derivatives

When benzo[ ]furan derived polycyclic phenol 84 was allowed to react with bromine, tribromide 85 was formed in high yield (Equation 65) <1999JME3199>. Reaction of 2-methylbenzo[ ]furan 86 with Wbromosuccinimide (NBS) at room temperature gives 3-bromo-2-methylbenzo[. ]furan 87 as illustrated in Equation (66) <2005JOC10323>. 

The cyciization of o-alkynyl phenol derivatives under the influence of a base or copper or palladium catalysts is a simple and reliable route to benzo[3]furans (Equation 107) <1996H(43)101>, given that the substrates are easily... 

The ring closure of orf/io-substituted phenols is a route to production of benzo[6]furans on an industrial scale. The natural benzo[6 ]furan derivatives karanjin, pongapin, khellin and visnagin have been prepared via the respective o-hydroxyarylacetaldehydes, whilst an extension to the cyclization of o-hydroxybenzyl alkyl ketones has made it possible to synthesize polycyclic benzo[6]furans under the influence of demethylating and dehydrating media. Pterocarpans have been synthesized from suitable isoflavones by this route. 

The allyl ethers of phenols may be converted via a Claisen rearrangement to o-allyl derivatives and thence to the benzo[6]furans. The products of addition of bromine to the o-allylphenols give good yields of the heterocycle on prolonged heating with alkali, but the photochemical rearrangement of O-allylphenol is not so effective. 

Rhodium(lll)-catalyzed redox—neutral coupling of N-phenoxyacet-amides and alkynes led to benzo[l)]furan derivatives (13AGE6033). Furo[2,3-l)]pyran-6-one derivatives were prepared via rhodium(II)-catalyzed reactions of diazo compounds and ethynyl compounds (13T9294). Copper-mediated oxidative annulation of phenols and unactivated internal alkynes afforded benzo[l ]furan derivatives (13CS3706). E t-kaurane maoecrystalV was produced via C-H functionalization (13JA14552). Rhodium-catalyzed intramolecular C-H... 

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