Naphthofurans synthesis

F.V. Singh, T. Wirth, Hypervalent iodine mediated oxidative cyclization of o-hydroxystilbenes into benzo- and naphthofurans. Synthesis 44 (2012) 1171-1177. 

Naphtho[2,3-c]furan, 1,3-diphenyl-thiophene synthesis from, 4, 904 Naphthofurans aromaticity... 

The three-component synthesis of benzo and naphthofuran-2(3H)-ones from the corresponding aromatic alcohol (phenols or naphthols) with aldehydes and CO (5 bar) can be performed under palladium catalysis (Scheme 16) [59,60]. The mechanism involves consecutive Friedel-Crafts-type aromatic alkylation and carbonylation of an intermediate benzylpalla-dium species. The presence of acidic cocatalysts such as TFA and electron-donating substituents in ortho-position (no reaction with benzyl alcohol ) proved beneficial for both reaction steps. 

The method has also proved to be applicable to the synthesis of polycyclic benzofurans naphthofurans from suitable naphthols,215 benzodifurans from Bz-hydroxybenzofurans,219 naphthodifurans from hydroxylated naphthofurans,228 thienobenzofurans from Bz-hydroxy-benzo[6]thiophenes.218,229... 

Kucklaender, U. Mechanism of the Nenitzescu reaction, IV. Synthesis of benzindole derivatives. Liebigs Ann. Chem. 1978,129-139. Kucklaender, U. Mechanism of the Nenitzescu reaction, V. Synthesis of naphthofuran derivatives. Liebigs Ann. Chem. 1978, 140-149. Kucklaender, U., Huehnermann, W. Studies on the mechanism of the Nenitzescu reaction. Synthesis of 6-hydroxyindole derivatives. Arch. Pharm. (Weinheim, Ger.) 1979, 312, 515-526. 

Regio-isomeric naphthofurans and benzodifurans were made by a base-catalyzed cyclization reaction from their corresponding o-alkoxybenzoylarenes as shown below <05T545>. An innovative synthesis of dibenzofurans through a carbanion-induced ring transformation reaction was so described <05TL491>. 

To convert labdanolic acid (8.27) to the naphthofuran (8.10), it is necessary to shorten the side chain and then cyclise the residue onto the alcohol to form the furan ring. In this synthesis, Bolster and de Groot carried out the chain shortening in two steps.816 Firstly, after protection of the ring hydroxyl group by conversion to the acetate, the terminal acidic carbon atom was removed by photo-decarboxylation in the presence of iodine and iodobenzene diacetate. This gave the iodinated material (8.29). Treatment of (8.29) with potassium tert-butoxide... 

Synthesis of optically active polytactic polymers from benzofuran and naphthofurans by polymerization in the presence of optically active catalysts... 

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