2,3,4- or 2,3,5-trisubstituted furans: catalyst-controlled highly regioselective ring-opening cycloisomerization reaction of cyclopropenyl ketones

2,3,4- or 2,3,5-trisubstituted furans were highly regioselectively formed from the cycloisomerization reaction of the same starting cyclopropenes 1 via the subtle choice of the transition metal halides. Under the catalysis of 5 mol % PdCl2(CH3CN)2, 2,3,5-trisubstituted furans 2 were given in 50-88% yields with 95-99% regioselectivities, while 2,3,4-trisubstituted furans 3 were formed in 78-96% yields with 99% regioselectivities under the catalysis of 5 mol % CuI.     

Synthesis of tetronic acid enamine. Dienamine derivatives from 3-(2H)furanones

The synthesis of 5-aryl (or alkyl) aminomethylene-3-(1-amino or 1-alkylaminoethylidene)-2,4-dioxo-(3H,5H)furans and 5-arylaminomethylene-3-(1-hydroxyethylidene)-2,4-dioxo-(3H,5H)furans (new 3-acetyltetronic acid derivatives) are described. The stereochemistry of these compounds from the ¹H nmr data is discussed.     

Pd0-catalyzed coupling cyclization reaction of Aryl or 1-alkenyl halides with 1,2-allenyl ketones: scope and mechanism. An efficient assembly of 2,3,4-, 2,3,5-tri- and 2,3,4,5-tetrasubstituted furans

Described herein is the Pd(0)-catalyzed coupling cyclization reaction of 1,2-allenyl ketones with organic halides leading efficiently and conveniently to not only 2,3,4- and 2,3,5-trisubstituted furans but also 2,3,4,5-tetrasubstituted furans. Furthermore, this method showed high substituent-loading capability and tolerance of various substituents. The reactions of 1,2-allenyl ketones 1 e, 1 p, 1 q, and deuterated [D]1 c were performed for a mechanistic study, which demonstrated that instead of an enolization pathway, the reaction may proceed via the intermediacy of dienolate palladium and intramolecular nucleophilic attack on the pi-allyl palladium intermediate by the carbonyl oxygen.     

Reaction of benzoxazolone with 2,4-dinitrochlorobenzene: Formation of 10-(2,4-dinitro)phenyl-3-nitrophenoxazine

Arylation of benzoxazolone 1 by 2,4-dinitrochlorobenzene 2 under solid-liquid phase transfer catalysis (PTC) gave 3-(2,4-dinitro)phenylbenzoxazolone 3 and 10-(2,4-dinitro)phenyl-3-nitrophenoxazine 4 . Neither PTC nor copper catalysis achieved arylation of 1 by less activated aryl halides.     

Alkylation of β-diketones through their co(II), co(III) and zn(II) complexes. 1-Bromoadamantane as alkylating agent.

α-(1-adamantyl)-β-diketones are now accessible by the alkylation of Co(II) complexes of β-diketones with 1-bromoadamantane. The intermediacy of adamantyl cation is proposed. Co(II), Co(III) and Zn(II) complexes of pentane-2,4-dione react with alkyl halides precursors of stabilized carbenium ions, to give 3-alkylpentane-2,4-diones.     

Preparation of furans from alkynols utilizing palladium catalyzed intramolecular addition of alcohol to acetylene as a key reaction

A procedure is described for the synthesis of furans from 3-alkyn-1,2-diols or 2-methoxy-3-alkyn-1-ols by palladium catalyzed intramolecular addition of alcoholic moiety to acetylene linkage followed by elimination of water or methanol. The intermediary 3-furylpalladiums can be trapped with allyl halides affording 3-allylfurans in good yields.     

Chemoselective synthesis of highly substituted 1,2-allenyl ketones, furans, and 2-alkynyl ketones from reaction of lithium selenolates with 1-(1-alkynyl)cyclopropyl ketones and electrophiles

A homo-Michael addition reaction of lithium selenolates with 1-(1-alkynyl)cyclopropyl ketones and the subsequent reaction with electrophiles such as PhSeBr, NFSI and NCS is reported. Based on the nature of electrophiles, this reaction may afford highly substituted 1,2-allenyl ketones or furans (E(+) = PhSe(+)) and 2-alkynyl ketones (E(+) = F(+), Cl(+), active halides) as the final products, respectively.     

Ruthenium-catalyzed coupling reaction of 2,3,5-trisubstituted furans with aryl halides through C-H bond cleavages

A variety of functionalized furans were synthesized by way of a ruthenium-catalyzed coupling reaction of 2,3,5-trisubstituted furans with aryl halides through C-H bond cleavages. The feature of the reaction was facilitative preparation of furan derivatives good functional group tolerance. All reactions gave the desired products in moderate to good yields (56-89%) in the presences of [RuCl₂(p-cymene)] and K₂CO₃ in NMP at 120 °C.     

Regioselective synthesis of 1-allyl- and 1-arylmethyl uracil and thymine derivatives

2,4-Bis(trimethylsiloxy) pyrimidines 1 with allyl halides and arylmethyl halides in 1,2-dichloroethane in the presence of I₂ regioselectively provide 1-allyl-/1-arylmethyl-uracil and thymine derivatives. The secondary aryl alkyl and diaryl methyl halides with 1 provide chiral 1-arylalkyl/1-(diarylmethyl) uracil/thymine derivatives. The procedure has been extended to the synthesis of fluorescent uracil/thymine derivatives.     

Highly substituted furans from 2-propynyl-1,3-dicarbonyls and organic halides or triflates via the oxypalladation-reductive elimination domino reaction

The palladium-catalysed reaction of 2-propynyl-1,3-dicarbonyls with organic halides or triflates provides an efficient straightforward entry into highly substituted furans. The best results have been obtained by using an excess of the alkyne. The process can tolerate a wide variety of important functional groups both on the alkyne and the organic halide or triflate. Under an atmosphere of carbon monoxide, the reaction affords furan derivatives incorporating carbon monoxide. Depending on the alkyne to organic halide or triflate ratio, acyl furans (incorporating one molecule of carbon monoxide) or enol esters (incorporating two molecules of carbon monoxide) can be isolated as the main products.     

Synthesis and reactions of benzo[b]furo[2,3-c]pyrylium salts

A method has been developed for the synthesis of 3-acetonyl- and 3-phenacylben-zo[b]furans by cyclization of 1-arloxy-2,4-pentanediones and 1-phenyl-4-aryloxy-1,3-butanediones in polyphosphoric acid. Acylation of 3-acetonyl(phenyl-benzo-[b]furans with aliphatic acid anhydrides in the presence of perchloric acid gives the benzo[b]furo[2,3-c]pyrylium perchlorates. The recyclization of the pyrylium salts with ammonia, aqueous alkali, and morpholine has been examined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 889–893, July, 1987.     

Gold-catalyzed efficient synthesis of 2,4-disubstituted furans from aryloxy-enynes

A series of (E)-1-aryloxy-1-en-3-ynes has been prepared by Sonogashira coupling of 2-bromo-3-aryloxypropenoates with terminal alkynes using Pd(PPh(3))(4) and CuI as the catalysts in Et(3)N. The resulting enynyl-aryl ethers are found to be highly applicable to the synthesis of 2,4-disubstituted furans with an ester group at C-4 position through an Au/Ag-catalyzed annulation reaction under extremely mild reaction conditions.     

Radical-polar crossover domino reactions involving organozinc reagents and β-(allyloxy)-enoates

Organozinc reagents (organozinc halides, diorganozincs and mixed copper-zinc reagents) react with β-(allyloxy)-enoates via a radical-polar crossover process to afford substituted furans in one single synthetic step following a domino reaction involving Michael addition and carbocyclisation. Reversal of diastereoselectivity can be obtained varying the organometallic and/or the reaction conditions.     

Asymmetric Hydrogenation of Furans and Benzofurans with Iridium–Pyridine–Phosphinite Catalysts

Enantioselective hydrogenation of furans and benzofurans remains a challenging task. We report the hydrogenation of 2‐ and 3‐substituted furans by using iridium catalysts that bear bicyclic pyridine–phosphinite ligands. Excellent enantioselectivities and high conversions were obtained for monosubstituted furans with a 3‐alkyl or 3‐aryl group. Furans substituted at the 2‐position and 2,4‐disubstituted furans proved to be more difficult substrates. The best results (80–97 % conversion, 65–82 % enantiomeric excess) were obtained with monosubstituted 2‐alkylfurans and 2‐[4‐(trifluoromethyl)phenyl]furan. Benzofurans with an alkyl substituent at the 2‐ or 3‐position also gave high conversions and enantioselectivity, whereas 2‐aryl derivatives showed essentially no reactivity. The asymmetric hydrogenation of a 3‐methylbenzofuran derivative was used as a key step in the formal total synthesis of the cytotoxic naphthoquinone natural product (?)‐thespesone.     

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.     

Palladium-Catalyzed Synthesis of 2,3,4-Trisubstituted Furans via Cascade Reactions of Aryloxy-enynes with Aryl Halides

A highly efficient palladium-catalyzed cascade reactions of aryloxy-enynes with aryl halides under mild reaction conditions has been developed. This methodology offers rapid access to 2,3,4-trisubstituted furans in good to excellent yields in a regioselective manner.     

3-aryl(alkyl)quinazoline-2,4(1<Emphasis Type="Italic">H</Emphasis>,3<Emphasis Type="Italic">H</Emphasis>)-diones and their alkyl derivatives

Two-stage reaction of methyl anthranilate with aryl(alkyl) isocyanates in keeping with the quantumchemical calculations and XRD analysis resulted in 3-aryl(alkyl)quinazoline-2,4(1H,3H)-diones that by treatment with alkyl halides, phenacyl bromides, esters and amides of chloroacetic acid were converted into the corresponding 1-alkyl derivatives.     

Syntheses of various 5-(3′-substituted phenyl)uracils

The Suzuki Pd(0)-catalysed coupling between arylboronic acids and aryl bromides or iodides in weakly alkaline medium has been used for the preparation of 5-(3′-chlorophenyl)-, 5-(3′-iodophenyl)-, 5-(3′-aminophenyl)-, 5-(3′-azidophenyl)-, 5-(3′-methylthiophenyl)- and 5-(3′-styryl)-substituted 2,4-di-t-butoxypyrimidines. In the coupling between 2,4 di-t-butoxy-5-pyrimidineboronic acid and the six different aryl halides that were used as coupling partners, only 1-azido-3-bromobenzene did not give satisfactory yields, 18%. The other five aryl halides gave the desired 5-(3′-substituted phenyl)-2,4-di-r-butoxypyrimidines in 41–92% yield. Dealkylation of these five 5-(3′-substituted phenyl)-2,4-di-t-butoxypyrimidines in 2.5M hydrochloric acid gave the corresponding 5-(bromoaryl)uracils in almost quantitative yields. 5-(3′-Azidophenyl)uracil was prepared in 43% yield directly from 5-(3′-aminophenyl)-2,4-di-r-butoxypyrimidine.     

Pentadienylsilanes as new reagents of the siteselective dienylmethylation of electrophiles promoted by a Lewis acid

(2,4-Pentadienyl)- and (2,4-hexadienyl)trimethylsilanes, prepared from the corresponding pentadienylpotassiums and trimethylchlorosilane, react smoothly with various electrophiles such as acetals, aldehydes and acid halides to give pentadienylation products, with regiospecific transposition of the pentadienyl group.     

Enantioselective Friedel–Crafts reactions of ethenetricarboxylates and substituted pyrroles and furans and intramolecular reaction of benzene derivatives

Compared to enantioselective Friedel–Crafts reactions of indoles, reactions of alkylidene malonates with monocyclic aromatic compounds generally proceed with low enantioselectivity. The Friedel–Crafts reactions of ethenetricarboxylates 1 and monocyclic heteroaromatic compounds, such as substituted pyrroles and furans were investigated. The reaction of 1 with 2,4-dimethylpyrrole in the presence of a chiral bisoxazoline–copper(II) complex (10 mol %) in tetrahydrofuran at room temperature gave alkylated products in up to 72% ee. The reaction of 1 with 2-substituted furans gave alkylated products in 46–62% ee. The absolute stereochemistry of the furan Friedel–Crafts product 7e was determined by transformation to the known 2,3-dimethylbutyric acid. The intramolecular reaction of benzene derivatives gave cyclized products up to 56% ee.