Palladium-catalyzed cyclization/Heck- and cyclization/conjugate-addition-type sequences in the preparation of polysubstituted furans

Palladium-catalyzed heterocyclization-coupling sequences have been developed starting from buta-1,2,3-trienyl carbinols and electron-deficient alkenes. Polysubstituted furans are formed where the heterocyclic ring originates from the elements of the butatrienyl carbinol while the electron-deficient olefin is incorporated as a C-3 substituent. In most cases, the reaction proceeds via a Heck-type pathway leading to the efficient formation of 3-vinylfurans. However, couplings with methyl vinyl ketone display a divergent behavior to afford selectively either Heck- or hydroarylation-type products depending on reaction conditions.     

A novel oxidation-ring-contraction of Hantzsch 1,4-dihydropyridines to polysubstituted furans

A novel oxidation-ring-contraction reaction took place when 4-substituted Hantzsch 1,4-dihydropyridines were treated with Oxone. This reaction pattern provided a convenient method for the synthesis of polysubstituted furans.     

Syntheses of polysubstituted furans: recent developments

Despite attracting tremendous interest for well over a century, the field of furan syntheses is continuously and rapidly developing. This brief overview highlights recent progress in the syntheses of polysubstituted furans primarily guided by substitution pattern. Accordingly, methods are categorized as providing access to either di-, tri- or tetrasubstituted furans.     

Cycloaddition reactions of polysubstituted furans with oxyallyl carbocations

New and improved routes to polysubstituted furans are described, together with a survey of their reactivity in cycloaddition reactions with oxyallyl carbocations, producing polysubstituted 8-oxabicyclo[3.2.1]oct-6-en-3-ones.     

Synthesis of polysubstituted furans via a novel and efficient heterocyclization approach

A new catalyst-free, one-pot synthesis of polysubstituted furans is reported. A series of [4-(4-aryl)-5-(cyclohexylamino)-2-(pyridin-2-yl)furan-3-yl](pyridin-2-yl)methanones was synthesized via multicomponent reaction of 1,3-di(pyridin-2-yl)propane-1,3-dione, aryl aldehydes, and cyclohexyl isocyanide.     

DABCO-catalyzed reaction of alpha-halo carbonyl compounds with dimethyl acetylenedicarboxylate: a novel method for the preparation of polysubstituted furans and highly functionalized 2H-pyrans

[Chemical reaction: see text] Polysubstituted furans and highly functionalized 2H-pyrans were prepared in good yields by DABCO-catalyzed reactions of alpha-halo carbonyl compounds with dimethyl acetylenedicarboxylate (DMAD) at room temperature.     

Facile synthesis of polysubstituted furans and dihydrofurans via cyclization of bromonitromethane with oxodienes

A series of polysubstituted furans and dihydrofurans have been prepared from readily available oxodienes and bromonitromethane in modest to excellent yields. This facile synthetic method is developed on the basis of proprietary properties of nitro group such as strong electron-withdrawing ability and cleavability. The conversion of nitro-substituted dihydrofurans to furans is presumably realized by elimination of HNO₂ under the aid of DABCO.     

Palladium-catalyzed one-pot synthesis of polysubstituted furans from alkynoates and 2-yn-1-ols

Easily accessible propargyl vinyl ethers are found to be acyclic precursors to construct furan derivatives. According to the reactive behavior of the substrates and the regulation of reaction conditions, three synthetic routes to polysubstituted furans via palladium-catalyzed reactions of propargyl vinyl ethers in situ-prepared from alkynoates and 2-yn-1-ols are presented herein. These methods could have potential application in synthetic and pharmaceutical chemistry for its facilitation and accessible starting materials.     

Intermolecular tandem addition-cyclization of bromoallenes: a facile synthesis of methylenecyclopropyl carboxylates and polysubstituted furans

The base-mediated reactions of 1,3-dicarbonyl compounds with bromoallenes used as an allyl dication equivalent were explored. The corresponding dimethyl methylenecyclopropane-1,1-dicarboxylates and 2,3,4-trisubstituted furans were efficiently synthesized. [reaction: see text]     

Synthesis of polysubstituted furans by palladium-catalyzed coupling of butatrienyl carbinols with aryl halides and triflates

An efficient one-pot two-step synthesis of polysubstituted furans is described using readily available 4,5-epoxy-2-alkynyl esters as starting materials. In the first step, reduction of these with SmI₂ affords buta-1,2,3-trienyl carbinol intermediates which, in the second step, participate in Pd(0)-catalyzed cyclization reactions with aryl halides and triflates by a mechanism probably involving oxidative addition, intramolecular oxypalladation and reductive elimination steps. In this manner, up to four carbon substituents are incorporated onto the furan ring, with the aryl group being introduced at the furan 3- or 4-positions. These features make the method particularly suitable for regioselective synthesis of tetrasubstituted furans.     

单糖脱水制备呋喃类化合物的研究进展

随着社会的发展,人类对能源的需求越来越多,但是地球上化石资源的储藏量逐渐减少,不可再生资源正面临枯竭,对人类的生存提出了挑战,寻找开发新型能源已迫在眉睫．众所周知,绿色化学。代表了当今化学工业的发展方向;绿色化学希望化合物的来源是绿色的,即源于那些可再生资源;其生产工艺环境友好,     

A green methodology for one-pot synthesis of polysubstituted-tetrahydropyrimidines using PEG

Abstract

Polyethylene glycol (PEG)-mediated facile one-pot synthesis of polysubstituted-tetrahydropyrimidines have been developed under mild and green reaction conditions. The obtained products are interesting nitrogen heterocyclic molecules that contain α- and β-amino acid blocks. PEG can be reused with minimum loss of its activity.     

Catalytic reductive debromination — A new method for the preparation of deutero-substituted thiophenes and furans

The principles of the reductive dehalogenation of a number of mono- and dibromosubstituted functional derivatives of thiophene and furan in the presence of a palladium complex applied to silica gel modified with -aminopropyl groups were investigated. A one-step method for the preparation of mono- and dideutero-substituted carbonyl compounds of the furan and thiophene series was developed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 176–180, February, 1982.     

Facile synthesis of 3a,6a-dihydro-furo[2,3-b]furans and polysubstituted furans involving dearomatization of furan ring via electrocyclic ring-closure

A facile and atom-economic method for the synthesis of 3a,6a-dihydro-furo[2,3-b]furan derivatives and polysubstituted furans starting from furylcarbionls has been developed. This protocol involved a domino Claisen rearrangement/dearomatizing electrocyclic ring-closure/aromatizing electrocyclic ring-opening sequence.     

Atom-economical chemoselective synthesis of 1,4-diynes and polysubstituted furans/pyrroles from propargyl alcohols and terminal alkynes

Under different conditions, the reaction of propargyl alcohols and terminal alkynes leads to the selective formation of 1,4-diynes and polysubstituted furans/pyrroles. Water is the only byproduct in the selective synthesis of 1,4-diynes and pyrroles, and the strategy for the furan synthesis is of 100% atom economy.     

A convenient preparation of 3-substituted furans: synthesis of perillene and dendrolasin

A variety of 3-substituted furans, including the natural products perillene and dendrolasin, are obtained in good yield via reductive annulation of 1,1,1-trichloroethyl propargyl ethers using catalytic Cr(II) regenerated by Mn/TMSCl. [reaction: see text]     

A convenient method for the preparation of 3-trimethylsilyl-2,5-dihydrofurans and their conversion to furans

Hydromagnesiation of 3-trimethylsilyl-2-propyn-1-o1 (1) followed by reaction with aldehydes or ketones affords (E)-3-trimethylsilyl-2-alken-1,4-diols (2), which can be readily dehydrated to 3-trimethylsilyl-2,5-dihydrofurans (3) by treatment with BF₃OEt₂. The compounds (3) are converted to furans (5) by epoxidation and subsequent treatment with H₂SO₄.     

A green and novel procedure for the preparation of ionic liquid

A green and novel procedure is described for the preparation of a series of ionic liquid containing alkylimidazolium-based or N-alkylpyridinium-based cations and hexafluorophosphate-based or tetrafluoroborate-based anions in one-pot solvent-free conditions to give excellent yields with shortened time.