2,3-Dihydronaphtho furan

Okamoto et al. [31] reported an enantioselective Rh-BINAP-catalyzed allyl ether isomerization-cycloisomerization domino sequence of phenol- or naphthol-linked 1,7-enynes 17 to give dihydrobenzofurans and dihydronaphtho-furans 18 (Scheme 12.9). 

The structural fragments B - J converge to 3,4,5-trimethyl-5,6-dihydronaphtho[2,3-/r]furan, K. Whether this is the 5(5)-or 5(7 )-enantiomer (as shown) cannot be decided conclusively from the NMR measurements. It is clear, however, that the 5-CiT proton at = 3.36 is split into a pseudo-quintet with 7.1 Hz, this is only possible if one of the 6-CH2 protons (at = 2.63) forms a dihedral angle of about 90° with the 5-CiT proton so that Jhh 0 Hz. 

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... 

The same intermediate occurs in the Lehmann method463 for converting the methiodides of phenolic Mannich bases into 2,3-dihydrobenzo-furans, through reaction with dimethyloxosulfonium methylide. Thus, o-benzoquinone methide (207) leads to 2,3-dihydrobenzofuran according to Scheme 4. Similarly, 2-naphtholgives l,2-dihydronaphtho[2,l-6]furan through 208 and 209, formed and rearranged in situ.i6i The reaction has been applied to the synthesis of polycyclic benzofurans.483,485... 

These methods have been applied to the synthesis of dihydronaphtho-[1,2-6], [2,1-6], and [2,3-6] furans and their substituted derivatives,491,496-499 and of the furoxanthone (234).500 A special case is the preparation of the benzofuran (235) as shown.501... 

The tandem 5-exo [67], and 6-exo-trig cyclization-SRNl [69] reactions afford 3-substi-tuted dihydrobenzofuranes and dihydronaphtho[2,l-k]furanes (28) for the former, and 4-substituted chromanes and benzo[f]chromanes (29) for the latter. In these reactions, at least one C—C bond is formed and the products obtained are feasible for further synthetic transformation (Scheme 10.53). Another approach to O-hetero-cycles is provided via SRN1 substitutions followed by a copper-catalyzed reaction (see Scheme 10.8). 

Vaillard, S.E., Postigo, A. and Rossi, R.A. (2002) Syntheses of 3-substituted 2,3-dihydrobenzofiiranes 1,2-dihydronaphtho [2,l-b]furanes, and 2,3-dihydro-l H-indoles by tandem ring dosure-SRNl reactions. Journal of Organic Chemistry, 67, 8500-8,506. 

The tandem sequence occurs between o-benzoylbenzyllithiums and furan-2-(5/7)-one168. The o-benzoyl-a-methoxybenzyllithium intermediate was generated by deprotonation of 2-methoxymethylphenyl phenyl ketone, 292, with LDA. Treatment of the a-lithiated product with furan-2-(5//)-one afforded the Michael addition/cyclization product, 293. The 9-aryl-9-hydroxy-3a,4,9,9a-tetrahydronaphtho[2,3-c]furan-l-(3//)-one 293 thus obtained was converted into the corresponding 9-aryl-4-methoxy-3a,4-dihydronaphtho[2,3-c]furan-] -(3//(-one 294 in good yield the subsequent dehydrogenation gave the desired product 4-methoxy-9-phenylnaphtho[2,3-c]furan-l(3/7)-one 295. 

The hydroxy group at position 2 in 1,4-naphthoquinone (318) is involved in [3 + 2] addition, producing the 2,3-dihydronaphtho[2,3-6]furan-4,9-dione 319 in 50% chemical yield (Scheme 6.140).1002 The reaction proceeds by a two-step process from a triplet excited quinone via exciplex (Section 2.2.3), intramolecular electron transfer (Section 5.2) and possibly ionic intermediate 320 formation. 

Diverse dihydronaphtho[l,2-(r]furans were generated fix)m 1,4-naphthoquinones and olefins in the presence of ceric ammonium nitrate (13OBC6097). ( )-Lantalucratins A and B were produced in the presence of diammonium cerium(IV) nitrate (13T10470).Benzo[(>]furan moieties were synthesized by a three-component Mannich reaction of 3-acetyl-2H-chromen-2-one or l-(l-benzo[fc]fioran-2-yl) ethanone with p-substituted aromatic aldehydes and aromatic amines with ceric ammonium nitrate (CAN) as a catalyst (13MCR4787).p-Alkenylphenols went through the oxidative dimerization to generate substituted dihydrobenzo[l)]furans in the presence of CAN (13T653). 

E-1-(5-Nitro-2-furyl)-2-p-tolylsulfoethylene, 45B, 330 Rubidium D-1,2-dihydronaphtho[2,1-b]furan-2-carboxylate monohydrate, 42B, 243... 

C14H12N2O2, 11-Oxa-5,1O-dicyano-6,9-dimethyltetracyclo-[6.2.1.0 . 0( ]undec 2-en-4-one, 43B, 240 Cl4H12O3, D-Methyl 1,2-dihydronaphtho[2,1-b]furan-2-carboxylate,... 

Odabas Z, Koc 1, Altindal A, Ozkaya AR, Salih B, Bekaroglu O (2010) Synthesis and electrochemical, in situ spectroelectrochemical, electrical and gas sensing properties of ball-type homo- and hetero-dinuclear phthalocyanines with four la,8b-dihydronaphtho b naphthofuro 3,2-d furan-7,10-diyl bridges. Synthetie Met 160(9-10) 967-977... 

The photolysis of the hypoiodites generated from the cyclobutanols, derived from the [2-l-2]-photo-addition of 2-hydroxynaphthoquinone with alkenes (A) and of 2-aminonaphthoquinone with vinyl arenes (B) in the presence of mercury(II) oxide and iodine induced regioselective P-fragmentations of the cyclobutanoxyl radicals to give a 2,3-dihydronaphtho[2,3-h]furan-4,9-dione and its [ l,2-h]furan-4,5-dione isomer (Scheme 76). 

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