2,3-disubstituted benzofuran derivatives

As depicted in the following scheme, in the presence of sodium iodate and pyridine, several 5,6-dihydroxylated benzofuran derivatives were synthesized via an oxidation-Michael addition of P-dicarbonyl compounds to catechols in a one-pot procedure <06TL2615 06JHC1673>. A novel additive Pummerer reaction of 2-benzo[fc]furan sulfilimines with carbon nucleophiles derived from P-dicarbonyl compounds was also employed to the synthesis of 2,3-disubstituted benzo[b]furans <06TL595>. 

A flexible and convergent access to 2,3-disubstituted benzo[b]thiophenes has been developed (Scheme 22). The most concise approach involves a sequential coupling of an o-bromoiodobenzene with benzylthiol and zinc acetylides leading to the adduct 78. Treatment with iodine followed by an iodine/magnesium exchange and acylation provides the polyfunctional benzofuran derivatives. a... 

This reaction has very broad applications in the preparation of the 2,3-disubstituted indole derivatives as well as pyrrole and benzofuran derivatives. 

The reaction of 2,5-disubstituted 3-furyl bromides with butyl-lithium and octafluorocyclopentene in dry tetrahydrofuran (THF) at —78°C gave bis(furyl)ethenes 82 (06JMC4690). Photochrome 83 (05JOC10323, 06EJ03105) (29-46% yield) and a series of its derivatives 84 (55-65%) containing different substituents at position 6 of the ben-zofuran ring were synthesized from 3-bromo-2-methyl-1-benzofuran (08JPP(A)146). 

Electrophilic substitution and metallation reactions of [l]benzothieno[3,2-3][l]benzofuran 63 were studied <2000CCC58>. Bromination, acetylation, benzoylation, formylation, and nitration usually afforded inseparable mixtures of 2- and 7-substituted derivatives as the main products. Disubstitution reactions preferably led to 2,7-disubstituted derivatives. [l]Benzothieno[3,2-3][l]benzofuran-10,10-dioxide 64 and [l]benzothieno[3,2-3][l]ben-zofuran-lO-oxide 65 can be selectively obtained by oxidation of 63. Mononitration of 64 and 65 led selectively to corresponding 7-nitro derivatives, respectively. Only sulfoxide 65 was successfully reduced. 

Tin Derivatives. A regiocontrolled method for construction of substituted benzofurans, dibenzofurans, benzothiophenes, and dibenzothiophenes uses 4-chloro-2,3-disubstituted-2-cyclobutenones as reactants together with a heterocycle (Scheme 17). In the construction... 

The reactions of 2,5-disubstituted 3-furyl bromides with butyllithium and OFCP in anhydrous THF at -78° afforded bisfurylethenes 76 [84]. Photochrome 77 [85, 86] (29 6 % yield) and a series of its derivatives 78 (55-65 % yield) with various substituents in position 6 of the benzofuran ring [87] were obtained from 3-bromo-2-methyl-1 -benzofuran. 1,2-Bis(5-n-aIkyl-2-phenyloxazol-4-yl)perfluorocyclopent-enes... 

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