Syntheses of Benzo[b]furan-6-carbonitrile and 6-Cyanobenzo[b]furan-2-boronic Acid Pinacol Ester

6-Cyanobenzo[b]furan-2-boronic acid pinacol ester (10) is a potentially useful two-point scaffold for the construction of specific compounds or compound libraries with benzofuran cores. Using a per-iodination/de-iodination strategy coupled with Sonogashira alkynylation and Cu-catalyzed heteroannulation, we have developed a procedure that allows the preparation of benzo[b]furan-6-carbonitrile (9) and 6-cyanobenzo[b]furan-2-boronic acid pinacol ester (10) in gram quantities.

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Synthesis and reactivity of 5-and 6-hydroxy-benzo[b]furan-2-selenolates

Treatment of 2,4-and 2,5-diacetoxyacetophenone semicarbazones with selenium dioxide gave 4-(2,4-and 2,5-diacetoxyphenyl)-1,2,3-selenadiazoles which were readily deacylated by the action of hydrochloric acid. 4-(2,4-and 2,5-Dihydroxyphenyl)-1,2,3-selenadiazoles thus obtained underwent decomposition in the presence of potassium carbonate in acetonitrile with formation of 5-and 6-hydroxybenzo[b]furan-2-selenolates which were subjected to alkylation.     

Condensed heterocycles. 42. Synthesis and some properties of 3-hydroselenobenzo[b]furan-2-carbaldehyde and 2-hydroselenobenzo[b]furan-3-carbaldehyde

The reactions of 3-chlorobenzo[b]furan-2-carbaldehyde and 2-bromobenzo[b]furan-3-carbaldehyde with sodium hydrogen selenide have yielded isomeric hydroseleno aldehydes which, under the action of atmospheric oxygen, have oxidized to diselenides, while alkylation of the seleno aldehydes with methyl iodide leads to the formation of the corresponding methylseleno derivatives.For communication 41, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1177–1179, September, 1984.     

Synthesis and Reactivity of 5-Alkoxybenzo[b]furan-2-selenolates

By reaction of selenium(IV) oxide with 5-alkoxy-2-hydroxyacetophenone semicarbazones4-(5-alkoxy-2-hydroxyphenyl)-1'2'3-selenadiazoles were prepared. The latter readily decomposed whentreated with potassium carbonate yielding 5-alkoxybenzo[b]furan-2-selenolates. The selenolates obtainedunderwent alkylation effected by monochloroacetamide, were arylated by 2'4-dinitrochlorobenzene. Theoxidation of selenolates with iodine furnished bis(5-alkoxybenzo[b]furan-2-yl) diselenides.     

The reaction of 2-arylsulfonyloxytropones and active methylene compounds The formation of 8-hydroxy-2H-cyclohepta[b]furan-2-one and 2-amino-8H-cyclohepta[b]furan-8-one derivatives

Reaction of 2-arylsulfonyloxytropones (IV) and active methylene compounds, diethyl malonate, ethyl acetoacetate, ethyl cyanoacetate, malononitrile or cyanoacetamide, in the presence of NaOEt give 8-hydroxy-2H-cyclohepta[b]furan-2-one derivatives (V) and/or 2-amino-8H-cyclohepta[b]furan-8-one derivatives (VII), in addition to azulene derivatives (1) or 2H-cyclohepta(b]furan-2-one derivatives (II), known to be obtained by the reaction of 2-chlorotropones or 2-methoxytropones with active methylene compounds. Relative yields of products are influenced markedly by conditions, e.g. base type or molar ratios. The formation of V and VII is characteristic of 2-arylsulfonyloxytropones, not being observed with 2-chlorotropones or 2-methoxytropones. A reaction course involving elimination of the arylsulfonyl group as arenesulfinate ion is presented.     

Synthesis of benzo[b]furan-2-thioles from 4-(2-hydroxyaryl)-1,2,3-thiadiazoles

4-(2-Hydroxyaryl)-1,2,3-thiadiazoles treated with bases decompose with nitrogen liberation and the formation of benzo[b]furan-2-thiolates. On acidifying the thiolates benzo[b]furan-2-thiols were obtained. 4-(4- and -5-Benzyloxy-2-hydroxyphenyl)-1,2,3-thiadiazoles formed analogously the corresponding benzo[b]furan-2-thiolates whose acidifying afforded polymeric compounds.     

New Calix[4]arene Based Hydroxystyryl Cyanine Dyes

Calix[4]arene derivatives bearing one or two hydroxystyryl cyanine chromophores at the wide rim of the macrocycle have been synthesized. The influence of bases and Li⁺ on the UV–Vis spectra of the compounds obtained has been investigated.     

A convenient synthesis of 2-arylidene-3,8-dihydro-2H-cyclohepta[b]furan-3,8-diones

3-(2-Bromoacetyl)tropolone ( 1 ) reacted with several benzaldehydes 2a-e to afford 2-arylidene-3,8-dihydro-2H-cyclohepta[b]furan-3,8-diones 3a-e in very good yields.     

Facile Total Synthesis of Benzo[b]furan Natural Product XH-14

An efficient and practical total synthesis of benzo[b]furan natural product XH-14 is demonstrated in nine steps from vanillin. Introduction of iodide substituents in the reaction including optimization of the reaction sequences is essential for the successful synthesis of XH-14. Sonogashira coupling with iodobenzene, iodine-induced cyclization, Wittig reaction, and formylation are critical in the high-yield total synthesis of XH-14.     

Synthesis of donor-acceptor chromophores by the [2 + 2] cycloaddition of arylethynyl-2H-cyclohepta[b]furan-2-ones with 7,7,8,8-tetracyanoquinodimethane

Arylethynyl-2H-cyclohepta[b]furan-2-ones reacted with 7,7,8,8-tetracyanoquinodimethane (TCNQ) in a formal [2 + 2] cycloaddition reaction, followed by ring opening of the initially formed cyclobutene derivatives, to afford the corresponding dicyanoquinodimethane (DCNQ) chromophores in excellent yields. The intramolecular charge-transfer (ICT) interactions between the 2H-cyclohepta[b]furan-2-one ring and DCNQ acceptor moiety were investigated by UV/Vis spectroscopy and theoretical calculations. The redox behavior of the novel DCNQ derivatives was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed their multistep electrochemical reduction properties depended on the number of DCNQ units in the molecule. Moreover, a significant color change was observed by visible spectroscopy under electrochemical reduction conditions.     

Electro-Organic Synthesis of 2-Amino-3-cyano-benzofuran Derivatives Using Hydroquinones and Malononitrile

Abstract

In this work, electrochemical oxidation of hydroquinones has been studied in the presence of malononitrile as a nucleophile in aqueous solution using cyclic voltammetry and controlled potential coulometry. The results indicate that the quinones derived from hydroquinones participate in Michael addition and then intramolecular nucleophilic addition to yield benzofuran derivatives. The electrochemical synthesis of these new 2-amino-3-cyano-benzofuran derivatives has been performed successfully at a carbon-rod electrode in an undivided cell in good to excellent yields at room temperature.     

(苯并呋喃-2-酰基)二茂铁衍生物的合成与表征

氯乙酰基二茂铁(1)与水杨醛或取代水杨醛在聚乙二醇-400作相转移催化剂条件下,使Williamson反应与Knoevenagel反应在一锅内完成,以40.2%～70.0%的总收率得到了由羰基相连的二茂铁与苯并呋喃组成的结构新颖的闭环产物(苯并[b]呋喃-2-酰基)二茂铁衍生物2a～2n.通过IR,1HNMR,MS和元素分析确认了所合成新化合物2a～2n的结构.     

One-Pot Solvent-Involved Synthesis of 5-O-Substituted 5H-Chromeno[2,3-b]pyridines

Chromeno[2,3-b]pyridines are substances demanded in medicinal and material chemistry. PASE (pot, atom, and step economy) and in particular one-pot approaches are key green chemistry techniques that are applied for the synthesis of heterocyclic compounds. In this case, the PASE approach was extended with ‘component economy’, as solvent was used also as reactant (solvent-involved reaction). This approach was adopted for the one-pot synthesis of previously unknown O-substituted 5-alkoxy-5H-chromeno[2,3-b]pyridines via two-step transformation, namely the reaction of salicylaldehydes and malononitrile dimer, with the subsequent addition of alcohol. The mechanistic studies revealed the possibility of concurrent reaction. The studies aided in optimizing the reaction conditions for the best yields (77–93%). Thus, the one-pot reaction proceeds efficient and quickly, and the work-up procedure (only simple filtering) is very convenient. The structure of synthesized chromeno[2,3-b]pyridines was confirmed by 2D NMR spectroscopy.