Arylfurans

Aqueous Diels-Alder reaction has also been applied at the industrial level. 2,2,5-Trisubstituted tetrahydrofurans 21 are a class of active azole antifungals. Workers at Schering-Plough [21] developed a synthetic approach based on a Diels-Alder reaction between 2-arylfurans 22 and ethyl acetylenedicarboxylate (Scheme 6.9). Under thermal conditions the reaction gave a low yield of... 

Monobromination of 2-arylfurans para-substituted by halogen or nitro gave high yields (75-84%) of 5-bromo products two molar equivalents of bromine led to 3,5-dibromination (77-96%). Presumably there is better charge delocalization for 3- than for 4-substitution (80CHE334). Ethyl 5-bromo-2-furoate has been made by a bromodesilylation process (91MI1). 

Treatment of 2-aryIfurans with ruthenium tetroxide leads to radical cations which form purple solutions of a charge transfer complex with the reagent. Oxidation of 2-arylfurans in a two-phase system with ruthenium tetroxide and aqueous hypochlorite yields products whose formation can be interpreted in terms of the radical cation intermediate (76CC890). 

Furans also form cyclic peroxides on reaction with singlet oxygen these undergo some interesting rearrangements as shown by the formation of the 2-aroyl enol esters 226 from the peroxides derived from 2-arylfurans. 

Tetrahydrofurans are accessible through hydrogenation of the furan nucleus. Substituent effects in the catalytic hydrogenation of dimethyl-2-arylfuran-3,4-dicarboxylates have been investigated (Scheme 50) <2000S2069>. A mild method for hydrogenation of aromatic heterocycles in aqueous media has been reported <2006SL1440>. 

The interaction of furan and aryldiazonium chlorides in the presence of alkali leads to 2-arylfurans, e.g., 2-phenyl-, 2-p-halophenyl-, and 2-p nitrophenylfuran however, the yields are low (15-22%). ... 

Cation-radicals from 2-arylfurans have been suggested to be involved in the oxidation of these compounds by ruthenium tetroxide. The suggestion is based on the observation of the capture by the heterocycle of the chlorine from chlorinated solvents and of a broad ESR signal which persists for several days. 

The thiazolium-mediated three-component reaction of thiazolium salts 201, aryl aldehydes and dimethyl acetylenedicarboxylate provides a facile synthesis of 2-amino-2-arylfurans 202 <05OL1343>. The reaction pathway may involve the sequential nucleophilic addition of thiazol-2-ylidene 203 with the aldehyde and DMAD to form the spirocyclic intermediate 204 through the simultaneous formation of two C-C bonds and a C-O bond Selective ring opening of the spirocyclic intermediate 204 followed by hydrolysis leads to 3-aminofuran 202 via 205. 

Arylfurans were prepared by reaction of 2-lithioiliran with unhindered aryl triflates in the presence of LDA <93JOC4722>. Alkylfuran-2-acetic acids are accessible by a regioselective ring opening reaction of anhydride 1 <93SL40>. 

Base-assisted cyclization of l-[3-[hydroxy(substituted methyl)]propargyl]benzotriazoles, which are available from lithiated 1-propargylbenzotriazole and aromatic aldehydes, gives 2-arylfurans (Equation (13)) <93JOC3038>. 

Yamamura s group developed a synthetic route to (jS-acylvinyl)azu-leno[l,2-l7]- or -[2,l-b]azoles, which is exemplified in Scheme 15. Stille coupling of thienylcycloheptatriene 52b with 2-alkyl- or 2-arylfuran derivatives (e.g., 52a) yields furylthiophenes (e.g., 53), which after... 

Reaction of the chloropyrazine 2 with furan afforded the 2-arylfuran. 2-Arylation of benzo[ >]furan (4) occurs with o-bromonitrobenzene (3) [3b]. Regioselective 2-arylation of ethyl 3-furancarboxylate with 3 occurred to give 5 in 80 % yield when Pd(PPh3)4 and AcOK were used in toluene. 5-Arylation was the main path when ligandless Pd/C was used in the polar solvent NMP. The furo[3,2-c]quinolinone 6 was obtained after hydrogenation of the nitro group [4]. 

Cyclopropylalkynes (27) readily react with hexacarbonylchromium to produce (3-cyclopropylpropynylidine)pentacarbonylchromium complexes (28) whose dimethyl-amine Michael adducts (29) undergo 3 -I- 2-cycloaddition with alkynes to yield cyclopropyl-substituted 3-ethoxy-5-dimethylaminocyclopentadienes (30) in very good yields (Scheme 11). A one-step synthesis of 2-arylfurans involves the cerium ammonium nitrate-mediated oxidative cycloaddition of cyclic and acyclic 1,3-dicarbonyl compounds to alkynes.The new chiral Ai-(ethynyl)allylglycines (31)... 

Saksena, A.K. Girijavallabhan, V.M. Chen, Y.-T. Jao, E. Pike, R.E. Desai, J.A. Rane, D. Ganguly, A.K., Aqueous Diels-Alder reactions of electron deficient 2-arylfurans a highly stereoselective route to 2,2,5-trisubstituted tetrahydrofurans towards a novel class of orally active azole antifungals, Heterocycles, 1993,35,129-34. 

Y.R. Lee, M.W. Byun, B.S. Kim, Efficient one-step synthesis of 2-arylfurans by ceric ammonium nitrate (CAN)-mediated cycloaddition of... 

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