Naphthofuran derivatives

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. 

A similar reaction of tertiary alkyl aminocrotonates leads to a mixture of isomeric naphthofuran derivatives (equation 92). 

Treatment of 1 with l-lithio-3-phenyl-l-propyne in THF at -78°C, yields 3-alky-nyl eyelobutenone 2 that after being refluxed in toluene gives naphthofuran derivative 3 in 45% yield (Seheme 24.1). 

Furan derivatives with an aromatic system fused on one of the ring s double bonds, such as benzofuran, naphthofuran etc., can be polymerized cationically through the other ring s double bond. In these polymerizations the complications encountered with furan and alkylfurans [see Section III-A-l-c] are absent because only one unsaturation is available for propagation, the other being tied up in the benzene system... 

The cyclisation of naphthyl propargyl ethers occurs efficiently under microwave irradiation leading to naphthopyrans, but naphthofurans are formed in the presence of base <96JCR(S)338>. The thermal rearrangement of naphthyl 3-trimethylsilylprop-2-ynyl ethers yields the 4-trimethylsilyl derivatives of naphthopyrans <96H(43)751>. 

Crounse and Desai29 showed further that 2-(/>-tolyl)benzo[6]furan with Schiff s base derived from terephthalaldehydic acid and aniline gives, on treatment with excess potassium r-butoxide, the corresponding stilbene carboxylic acid. Schiff s base derived from phthalaldehydic acid and aniline exists30 as the 3-anilinophthalide (40). Nevertheless, this also reacts similarly with, for example, the naphthofuran (39) to form 2-(2 -carboxystilben-4-yl)naphtho [ 1,2-6]furan (41).29 Analogous car-... 

Pd-catalyzed reaction of a-n hthol, isobutyraldehyde, and CO in the presence of CF3CO2H afforded naphthofuran-2(3/7)-one 28 in 79 % yield. The reaction is explained hy acid-catalyzed formation of l-(2-naphthyl)butanol 27, followed by carbonylation of the benzylic alcohol. Although its reactivity is lower, the phenol derivative 29 reacted with acetaldehyde to generate the benzylic alcohol 30, which was carbonylated to provide the benzofiiranone 31 in 54% yield [14]. 

Reaction with Quinones and Naphthoquinones. Naphth-acene-5,12-diones and naphtho[2,3-c]furan-4,9-diones can be obtained by Mn(OAc)3-promoted reaction between 2-benzoyl-1,4-naphthoquinones and 1,3-dicarbonyls (eq 32). Electron-withdrawing groups on the benzoyl moiety will favor the naph-thofurane derivatives. Higher selectivity is also observed as the size of the 1,3-dicarbonyl substituent (R) increases. Naphthofu-ranes will also be favored in neutral solvents or if the reagents are heated with sodium acetate prior to the reaction with Mn(OAc)3. In contrast, naphthacenediones will be favored if the reaction is carried out in formic acid. An intramolecular variant of this reaction exists and furnishes the naphthacenediones in higher yield, only trace amounts of naphthofuranes are observed (eq 33). ... 

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