Furans Naphthofurans

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

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... 

Naphthofurans have been synthesized from the corresponding naphthols thus 2-methoxy-3-allylnaphthalene (from allyl bromide and 3-lithio-2-methoxynaphthalene) gives 2-methyl-2,3-dihydronaphtho-[2,3-6]furans,435 and l-allyl-2-naphthol gives (with pyridine hydrochloride) 2-methyl-2,3-dihydronaphtho[2, l-6]furan.438... 

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-... 

These natural substances range from simple monosubstituted benzo-furans, such as 5-methoxybenzofuran (44) (which has bactericidal propertiesand plays an important part in the biosynthesis of natural benzofurans ) to more complex benzofurans. They include polycyclic compounds with one naphthofuran or phenanthrofuran ring (tanshinones, etc.) and furanic diterpenes [methyl vinhaticoate (45), methyl voucapenate (46), viridine (47)i5o-i52 fungicidal metabolite)]. 

Naphthofuran, methyl-Naphtho[1,2-6]furan Naphtho[1,2-6]furan, dimethyl-Naphtho[1,2-6]furan, 2-methyl-Naphtho[2,1-6]furan... 

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... 

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). ... 

Similar results have been obtained by polymerization of a or j3-naphthofuran (LXXIV) [200]. Like benzofuran, these monomers are not dissymmetric and it is only when the molecule has reacted that a sequence of asymmetric carbon atom is formed along the main chain they polymerize very easily in presence of aluminum chloride or titanium tetrachloride and j3-phenylalanine the use of c/-alanine or /-histidine as co-catalyst always leads to polymers with no optical activity both for benzo- and naphthofurans. Polynaphto-furan can be crystallized by thermal treatment, in contrast to polybenzofuran and its structure, at least partially, must be considered isotactic. This last work dates back to 1966. Since that time, no other results have been published in this field. 

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