Naphthofurans

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

The naphthofuran with the same substituent in the heterocycle reacts with dimethyl acetylenedicarboxylateto give dimethyl 2-(A,-methylanilino)-l-naphthoxepin-3.4-dicarboxylatc (2) in 57% yield.180,181... 

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 behaviour of naphthofurans was found to be entirely similar to that of benzofuran68. ... 

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>. 

When the acetate (9) and (11) were treated with acid, retro-aldol, aro-matization and dehydration reactions would take place and the final products (10) and (12) were formed. The structures of (10) and (12) have been proved to be naphthofurans U). 

Ohmae and Katsui irradiated vitamin K-l (82) in alcoholic solution with UV light and obtained the hydroperoxide (85), its corresponding hydroxide and the ketone (89). Also isolated were phthiocol (90), the naphthofuran (91) and polymeric material [69], Similar irradiation in benzene gave (89) and (91) [70],... 

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... 

In the naphthofuran series, monoacetyl anhydronorjavanicin (131) has been synthesized from the o-hydroxyarylacetone norjavanicin.332... 

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... 

R5 = R7 = F, R6 = OMe).684 These various methods have also been applied to the naphthofuran series.283,685,686... 

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-... 

Meta-chloroperoxybenzoic acid or osmiumtetroxide/sodium periodate chromic acid anhydride in acetic acid or acetic anhydride give good results with the benzofurans, but was unsatisfactory in the naphthofuran (VIII/172, R-R, CH= CH-CH=CH-) series. Ozonolysis, however, was very effective with both types of compounds (yields 63-86%). 

A similar reaction of tertiary alkyl aminocrotonates leads to a mixture of isomeric naphthofuran derivatives139 (equation 92). 

Propargyl naphthyl ethers can be rearranged to to naphthofurans in shorter reaction times when exposed to microwave irradiation (Scheme 89) <1996JCM338>. These alkynes first undergo Claisen rearrangement to form an allene intermediate which in turn spontaneously cycloisomerizes to the benzofuran product. 

MethylT2,l-f)]naphthofurane (4) was obtained by this method from l-allyl-2-naphthol (3). 

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)]. 

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