Alexander V. Butin

Furan ring opening—indole ring closure: a new modification of the Reissert reaction for indole synthesis ☆

Abstract A new modification of the Reissert reaction is reported. On treatment of 2-tosylaminobenzylfurans with ethanolic HCl, some indole derivatives have been obtained. The furan ring served as the origin of a carbonyl group in this reaction.

A Simple Route to Polysubstituted Indoles Exploiting Azide Induced Furan Ring Opening

A straightforward, efficient indole synthesis based on thermolysis of 2-(2-azidobenzyl)furans with attack of the formed nitrene moiety onto the ipso position of furan ring has been developed. The cyclization is accompanied by furan ring opening and affords indoles with a 2-acylvinyl substituent suitable for further modifications.

o-Nitroaryl-bis(5-methylfur-2-yl)methanes as Versatile Synthons for the Synthesis of Nitrogen-Containing Heterocycles

2-Nitroaryldifurylmethanes 1a and 1b, readily available by condensation of 2-nitrobenzaldehyde and 6-nitroveratraldehyde with 2-methylfuran, were transformed into indole, cinnoline and benzothiazine-3,1 derivatives. The reduction of 2-nitroaryldifurylmethanes gave the corresponding anilines 2a,b or indole 3 depending on the reaction conditions. A plausible mechanism for the last reaction involving intramolecular heterocyclic addition between a nitroso-group and a furan ring is proposed. Diazotisation of the amine 2b gave a cinnoline derivative - a product of intramolecular oxidative furan ring opening. Treatment of isothiocyanates 7a,b with perchloric acid resulted in a new rearrangement with furan ring migration leading to the 4-Hbenzothiazine-3,1 derivatives.

Furyl(aryl)alkanes and Their Derivatives. 19*. Synthesis of Benzofuran Derivatives via 2-Hydroxyaryl-R-(5-methylfur-2-yl)methanes. Reaction of Furan Ring Opening - Benzofuran Ring Closure Type

2-Hydroxyaryl(5-methylfur-2-yl)alkanes synthesized by alkylation of 2-methylfuran with various 2-hydroxybenzylic alcohols, were rearranged into corresponding 3-R-benzo[b]furan derivatives by treatment with ethanolic HCl solution. These compounds can not be transformed into dibenzoxazulenium salts.

Furyl(aryl)methanes and their Derivatives. Part 21: Cinnoline Derivatives from 2-Aminophenylbisfurylmethanes

Abstract (Z)-4-[4-(5-Methyl-2-furyl)-3-cinnolinyl]-3-buten-2-ones and (Z)-1-[4-(5-ethyl-2-furyl)-3-cinnolinyl]-1-penten-3-ones have been obtained from 2-aminoarylbisfurylmethanes under treatment with isoamyl nitrite/trimethylchlorosilane in dry acetonitrile. Intramolecular cyclisation and furan oxidative ring opening follow the formation of an intermediate diazonium salt. X-Ray analysis proved the cis-configuration of the alkene side chain.

Acid Catalyzed Reactions of Substituted Salicylaldehydes with 2-Methylfuran

Data, concerning condensation reactions of salicylaldehydes and 2-methylfuran are generalized. During the course of investigation a sequence of proceeding transformations is established. It is shown that it is possible to obtain 2-hydroxyarylbis(5-methylfur-2-yl)methane, benzofuran or oxazulene derivatives selectively by simple changing of the reaction conditions.

New Synthesis of 3-(2-Furyl)phthalides

Abstract3-(2-Furyl)phthalides were synthesized for the first time by the reaction of 2-formylbenzoic acids with furan derivatives in the presence of an acidic catalyst. It was found that the reaction of 2-formylbenzoic acids and 2-alkylfurans in aqueous dioxane in the presence of perchloric acid leads to a mixture of 2-carboxyaryldifurylmethanes and 3-furylphthalides, which can be separated easily by preparative column chromatography.

Effective Synthesis of 3-(2-Furyl)Phthalides Under the Friedel–Crafts Reaction Conditions

3-(2-Furyl)phthalides, or 3-(2-furyl)-2-benzofuran-1(3Н)-ones, are key starting materials for the synthesis of 2-(2-carboxybenzyl)furans [1], which can be used for the preparation of a whole range of biologically active heterocyclic systems. In particular, such compounds include the natural naphtho[2,3-b]furan4,9-diones [2] possessing cytotoxic and antiparasitic activity [3], as well as isocoumarin [4], isoquinolone [5] and pyridazinoisoquinolone [6] derivatives. The majority of currently known methods for the syntesis of 3-(2-furyl)phthalides are based on directed ortho-metalation of benzamides, achieved by the use of expensive organometallic reagents at low temperatures (down to -78°С) and under inert atmosphere [2, 7]. These limitations and the associated need for specific laboratory equipment present an obstacle to the wide use of 3-(2-furyl)phthalides in organic synthesis. At the same time, it is known that 3-(aryl)phthalides can be obtained by condensation of 2-formylbenzoic acids and arenes under the Friedel–Crafts reaction conditions [8-10], and 3-(3-indolyl)phthalides are synthesized similarly [11]. Previously, we have observed that synthesis of aryldifurylmethanes 4 by condensation of 2-formylbenzoic acids 1 with 2-(tert-butyl)furan (2d) in dioxane in the presence of HClO4 gave also 3-(2-furyl)phthalides 3 with 20-35% yields as by-products [12]. Addition of water to the reaction mixture (12% of the solvent volume) allowed to increase the yields of phthalides up to 35-40%. 3-(2-Furyl)phthalides were also successfully prepared starting from 2-methylfuran (2b), but the product yields did not exceed 25% in this case [13]. In the current study, we found that using water as solvent and hydrochloric acid as catalyst in combination with milder reaction conditions (room temperature) directed the process mainly towards the formation of 3-(2-furyl)phthalides 3. Insignificant amounts (no more than 10%) of aryldifurylmethanes 4 were formed as by-products [12], except for the reaction between 2-formylbenzoic acid (1a) and furan (2a), in which case the formation of an insignificant amount of tarry products in the reaction mixture was observed, while the product 4a was not detected at all. ______ *To whom correspondence should be addressed, e-mail: pasfreak@hotmail.com.

Synthesis of amines of the di-and trifurylmethane series

Methods are proposed for the synthesis of amines of the di-and trifurylmethane series-prospective compounds for the production of polymers and macrocyclic molecules-on the basis of 2-(2-furylmethyl)-1,3-isoindolinedione.

Polyfuryl(aryl)alkanes and their derivatives. 7. New recyclization and cyclization reactions in the 2-hydroxyaryldifurylmethane series

Reaction of 2-hydroxybenzaldehydes with α-methylfuran (sylvan) under acid-catalysis conditions was investigated. It is shown that the reaction does not stop at the step involving formation of 2-hydroxyarylfuryl-methanes but proceeds further with opening of one of furan rings and recyclization to 3-furylbenzo-furan derivatives. The latter in turn undergo transformations that lead to new heterocyclic systems — 5,6-dihydro-2,4-dimethyl-4-(5-methyl-2-furyl)-4H-benzo[b]furo[2,3-h]cyclopenta[b]furans. Data from the IR, PMR, and mass spectra, alternative synthesis, and x-ray diffraction analysis were used to confirm structures of the synthesized compounds.