Benzo difuran

Pyrolysis of tri-, tetra-, and penta-chlorobenzenes affords mixtures of chlorinated dibenzofurans and dibenzo-p-dioxins, " and chlorinated diphenyl ethers cyclize in the presence of palladium acetate to polychloro-dibenzofurans/ The action of malononitrile on tetrahydroxy-p-benzoquinone leads to the benzo-difuran (79), contrary to a previous report/ The acid-catalysed condensation of quinones with phenols has been studied p-benzoquinone and resorcinol, for example, afford compound (80)/ Naphtho[2,3- >]furan-4,9-diones (81 R = Me or Ph R = Ac, Bz, C02Et, or CN) are obtained from 2,3-dichloronaphtho-1,4-quinone and compounds R COCHaR in DMF that contains potassium fluoride/ The action of mineral acids on p-benzoquinone produces a mixture of complex benzofurans, which includes (82) and (83)/ Bases convert the ben-zofuranone (84) into the tetrameric compound (85), contrary to an earlier... 

The isomeric 2,3,6,7-tetrahydrobenzo[l,2-/ 4,5-/ ]difuran is also oxidized using an excess of DDQ to produce the fully conjugated benzo[l,2- 4,5-/ ]difuran 107 in 64% yield <2001JME1003>. 

Two furo-annelated benzo[c]furans, a benzo[2,l-Z) 3,4-c ]difuran (341) and a benzo[1.2-/ 3,4-c ]difuran (344) have been described. Acid-catalyzed ring closure of bisfuran 340, which is available from trans-trans-1,4-dibenzo-ylbutadiene (339) and /ranx-dibenzoylethylene. yields 341 in 83% yield. An independent synthesis which starts from 4-benzoyl-2-phenylfuran (343) is outlined in Scheme 21 the isomeric compound has been obtained similarly (Scheme 22). 

Cycloocta[l,2-c 5,6- ]difuran (291), a 16 n-electron analog of benzo[c]-furan, has been obtained by a Wittig reaction as a colorless crystalline solid (mp 131-133°C), rapidly becoming orange in air. In the absence of air the compound is stable. Thus, treatment of 291 with an excess of dimethyl fumarate in boiling benzene for 96 hr gave 76% of adduct... 

High yields of tricyclic compounds, 4,8-dihalo- or 4,8-dinitro-substituted 1,1,3,3,5,5,7,7-octa-fluoro-5,7-dihydro-l//,3//-benzo[l,2-c 4,5-c ]difurans 13, are obtained by treatment of the dihalo- or dinitrobenzene-1,2,4,5-tetracarboxylic acids with sulfur tetrafluoride and hydrogen fluoride at elevated temperatures.132 141... 

The 2,3-dihydrobenzo[l,2-7 5,4-3 ]difuran 705 can undergo a cycloaddition reaction with tetrazine 706 followed by furan ring opening and lactonizaton to afford the pyridazino-fused coumarin 707 (Scheme 174) <2005T4805>. Similarly, benzo[l,2-3 5,4-7 ]difurans 708 react with tetrazine 706 to form the pyridazino-fused coumarins 709 and 710 (Equation 283) <2005T4805>. 

An intramolecular reaction of an isocyanate on a benzo[l, 2-b 4,3-6 ]difuran constructed a fused pyridine ring, probably via a pericyclic reaction <86JHC1637>. Photolysis of the bisthiadiazoloquinone... 

The synthesis of the benzo[l, 2-b 4,5-6 ]difuran (56) is a variation of a common approach involving base-catalyzed cyclizations <87CA(106)176085>. Other variations formed 2-nitrobenzodifurans by cyclization of o-nitromethoxy aldehydes <87CA(107)211476>. The acidity of the 5-methyl protons in the bismethylthio dialdehyde (57a) allowed base-catalyzed cyclization to the benzo[2,l-6 3,4-6 ]dithiophene (58) <91BSB1>. 

The acid-catalyzed cyclization of appropriate aryloxyketones formed benzo[l,2-6 5,4-6 ]difuran and benzo[ 1,2-6 4,5-6 ]difuran (63BSF1003). Another variation involved the cyclization of an aryl thioacetal to a benzo[l,2-6 4,5-6 ]dithiophene <86CB3198>. In investigations of the synthesis of a unit of the CC-1065 skeleton (see Section 7.21.12), a carbene derived from the azo-compound (59) constructed the cyclopropano-fused benzodipyrrole (60) by simultaneous formation of the heterocyclic ring and the cyclopropane ring <83TL4773>. 

Benzo[l, 2-c 3,4-c ]difurans (85) can be formed by the rhodium-catalyzed intramolecular [2 + 2 + 2]cycloaddition of some triynyl ethers (84) <88JCS(P1)1357>... 

Irradiation of macrocycles having two l,5-dibenzoyl-2,4-dialkoxybenzene moieties with a 350 nm mercury lamp followed by dehydration afforded benzo[l,2-b 5,4-fc ]difuran-containing cyclophanes via a quadruple photocyclization in a one-pot operation as illustrated in the following scheme <02H(57)657>. Facile routes for the synthesis of novel cyclophanes containing both benzo[ 1,2-b 5,4-b ]difuran and naphthalene rings were developed in a similar manner <02JCS(P1)310>. 

Table 3 3 Kamlet-Taft parameter obtained with 3-(4-amino-3-methyl-phenyl)-7-pheyl-benzo[l,2-h 4,5-h ]-difuran-2,6-dione as a probe and n with 4-tert-butyl-2-(dicyanomethylene)-5-[4-(diethylamino)benzyhdene]A3-thiazohne (two evaluation methods, for details see [119])...

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