Furan ring opening—indole ring closure: pseudooxidative furan ring opening in the synthesis of indoles

A new approach to the synthesis of 4-(2-indolyl)-3-buten-2-ones is described based on condensation of 2-tosylaminobenzyl alcohols with N-tosylfurfurylamine. Pseudooxidative furan ring opening occurred via protolytic elimination of tosylamide from the side chain of the 2-tosylaminoaryl(5-tosylaminomethylfur-2-yl)methanes formed in situ.     

Synthesis of steroidal saponins bearing an aromatic E ring

A facile synthetic approach toward the steroidal saponins bearing an aromatic E ring was developed starting from the readily available spirostan saponin.     

An efficient synthesis of 2-(guaiazulen-1-yl)furan derivatives via intramolecular Wittig reactions

An efficient and mild synthesis of 2-(guaiazulen-1-yl)furans,starting from easily accessible 1-(3-aryl-2-cyanopropenoyl) guaiazulenes,tributylphosphine and acyl chlorides,is described.The strategy employs the intramolecular Wittig protocol as a key step to append the crticial furan ring,leading to the highly functional furans in good yields.     

Diastereoselectivity in the Paternò-Büchi reaction on furan derivatives

The reaction of benzoin, 4,4^′-dimethoxybenzoin and benzoin ethyl ether with furan gave the corresponding adduct with high diastereoselectivity (71-100%). The diastereoselectivity was explained considering the relative stability of the biradical intermediates. Benzofuran reacts with (S)-1-methylpropylbenzoylformate to give the corresponding adduct with de = 58%. The diastereoselectivity was explained considering the relative stability of the biradical intermediates.     

Microwave-mediated intramolecular Diels-Alder cyclization of biodihydroxylated benzoic acid derivatives

The synthetic utility of biodihydroxylated benzoic acid derivatives for the construction of bridge bicyclo scaffolds was investigated. Biodihydroxylation of benzoic acid using Ralstonia eutropha B9 gave (1S,2R)-1,2-dihydroxycyclohexa-3,5-diene-1-carboxylic acid (DCD) in high optical purity (>95% ee). Protection of the intermediate and subsequent functional group transformation gave the required cyclization precursors in moderate to excellent overall yields. Subsequent intramolecular Diels-Alder cyclization of biodihydroxylated benzoic acid derivatives was carried out using either thermal or microwave conditions. Enantiomerically pure products with five chiral centers were obtained in 4-6 steps from achiral starting material.     

Synthesis of 2,4-disubstituted 3-chlorofurans and the effect of the chlorine substituent in furan Diels-Alder reactions

2,4-Disubstituted 3-chlorofurans were synthesized in 42-69% overall yields by CuCl/bpy-catalyzed halogen atom transfer radical cyclization of 1-substituted 2,2,2-trichloroethyl allyl ethers to 2-substituted 3,3-dichloro-4-(1-chloroalkyl)tetrahydrofurans followed by base promoted dehydrochlorination. Diels-Alder reactions of 4-substituted 2-(2-furyl)-, 2-styryl-, and 2-crotyl-3-chlorofurans with dimethyl acetylenedicarboxylate occurred exclusively on the chlorofurano diene moieties and not on the non-chlorinated furano diene or the chlorinated exocyclic diene alternatives, demonstrating the predominance of the halogen effect in the furan Diels-Alder reaction.     

Design, synthesis and photo-cross-linking of a new photosensitive macromonomer from tetra-branched poly(ethylene oxide)s

A general procedure to increase the amount of photoreactive chromophore groups per oligoether chain is presented. In this work, a photoreactive macromonomer with four functionalities was synthesized by a four-step synthetic pathway with high yield. The photochemical behavior of this compound was studied with a view to obtaining polymeric networks. The significant advantage in this strategy is that the preparation of this material has as last operation, the obtaining and processing of polymer as thin film. In this way, the synthetic strategy based on assembling: (i) the polyether chains, (ii) a film forming backbone, and (iii) a photoactive moiety to be used for cross-linking, seems a viable solution to the problem of the continuous processing of materials.     

Synthetic studies of GKK1032s: the asymmetric synthesis of the decahydrofluorene skeleton via a novel cyclization of silyl enol ether and sequential retro Diels-Alder and intramolecular Diels-Alder reactions

GKK1032s, which were isolated from the culture broth of Penicillium sp. GKK1032, exhibit antitumor activity. We constructed the fully elaborated decahydrofluorene skeleton of GKK1032s. The C-ring was constructed by intramolecular cyclization reaction between a chiral epoxide and silyl enol ether, and the dienophile moiety was introduced concurrently. In addition, the AB-rings were stereoselectively constructed using novel sequential retro Diels-Alder (DA) and intramolecular Diels-Alder (IMDA) reactions. Several further modifications of the IMDA adduct were carried out, leading to the asymmetric synthesis of the desired hydroxyester including nine stereo centers.     

Concomitant ring contraction cyclization strategy for the synthesis of novel 4-oxo-4,5-dihydro-pyrroloquinolines

The synthesis of novel substituted pyrroloquinolinones is described by concomitant ring contraction cyclization form 2-(2-amino-5-nitro-phenyl)-[4H]-1,3-thiazines, which were derived from N-substituted 5-nitro-anthranilonitrile. An easy access to novel 4-thiono-1,4-dihydro-1,3-quinazoline heterocycles is also mentioned.     

Copper-catalyzed tandem intramolecular cyclization/coupling reaction: solvent effect on reaction pathway

In this study, we developed direct methods for the synthesis of 3-substituted indoles from o-alkynylanilines by utilizing a copper-catalyzed tandem intramolecular cyclization/coupling reaction under mild and simple reaction conditions. Our investigation revealed that choice of the aprotic polar solvents and additives such as camphorsulfonic acid is critical in this reaction.     

Novel formation of a bridged bicyclic furan by rearrangement of a tetrahydroxydecalinone

In the course of a synthetic approach to the arisugacins, we prepared the tetrahydroxydecalinone 8a (which exists as the hydroxytetrahydrofuran 8b) by a straightforward route from hydroxy-β-ionone. On treatment with mesyl chloride and base, the desired mesylate 9 was not formed but rather 8ab underwent a novel rearrangement to produce the bridged bicyclic furan 10 in excellent yield. A reasonable mechanism for the rearrangement is presented involving a retro-aldol reaction, a base-catalyzed β-elimination, and final furan formation from a β-hydroxymethyl enone.     

Studies into the generation and Diels-Alder reactions of 7,8-quinolyne with furan dienes

Reaction of an appropriate ortho-halo tosylate precursor with organolithium reagents provides the first conclusive route to the intermediate, 7,8-quinolyne. The transient existence of this hetaryne was confirmed by Diels-Alder reactions with furan derivatives that provide endoxide adducts. Chemical induced rearrangement of these adducts allows entry to key compounds of 10-hydroxy[h]benzoquinoline and its 7-substituted derivatives in modest yields.     

三氯化镱催化丙烯酸酯与呋喃成环反应的研究

D iels-A lder反应具有立体专一性和很好的区域选择性,已被大量应用于天然有机化合物、香料、药物等的合成中。一般说来,D iels-A lder反应在加热条件下即能发生,但加热往往导致反应的区域选择性和立体专一性下降,而研究表明,路易斯酸催化下的D iels-A lder反应在不同程度上表现出或反应速度加快,或产率提高,或条件温和,尤其是区域选择性和立体专一性得到提高等良好特性。呋喃类化合物由于呋喃环所具有的芳香性而较难与一般的亲双烯发生D iels-A lder反应。如呋喃和丙烯酸甲酯在加热条件下反应2~3个月,产率只能达到50%,且反应温度的提高…     

Base-controlled selective construction of polysubstituted dihydrofuran and furan derivatives through an I2-mediated cyclization

A base-controlled formal [3 + 2] cycloaddition of 1,3-dicarbonyl compounds to enones via an I₂-mediated cyclization was reported. Highly functionalized dihydrofurans and furans were selectively obtained under I₂/DMAP and I₂/DBU conditions in the cyclization step, respectively.     

Pd(0) catalyzed intramolecular alkylation: stereoselective synthesis of furan and isoxazoline-2-oxide analogs

New optically pure isoxazoline-2-oxide and furan analogs have been synthesized using Pd(0) catalyzed intramolecular cyclizations. Starting from a meso-diol, optically pure compounds were prepared without utilizing chiral ligands at any stage of the synthesis. The stereochemical outcome of the product (>99% ee) was influenced by desymmetrization catalyzed by Pseudomonas cepacia lipase and the stereoselective nature of the palladium catalyzed transformations.     

Sodium borohydride or potassium carbonate-mediated intramolecular Michael addition: a general method for the synthesis of fused dihydrofuran and furan derivatives

A simple and convenient method for the synthesis of fused dihydrofuran derivatives using NaBH₄-mediated reductive cyclization and fused furan derivatives by K₂CO₃-mediated intramolecular Michael addition followed by acid-catalyzed methanol elimination has been developed.     

A synthetic approach toward taxol analogs: studies on the construction of the CD ring

Tricycle 6, containing the CD ring of taxol, is constructed from (S)-(+)-carvone in 21 steps involving a Diels-Alder reaction with isoprene, a Baeyer-Villiger oxidation, an Oppenaurer oxidation and Meerwein-Ponndorf-Verley reduction, a stereospecific Grignard addition, and an intramolecular S_N2 reaction as the key steps.     

A furan ring expansion approach to the synthesis of novel pyridazino-psoralen derivatives

A convenient preparation of the parent tetrahydrobenzodifuran 2 was developed from resorcinol. The oxidation of one or both furan rings of this key intermediate was accomplished with DDQ and the resulting benzodifuran was subsequently reacted with 3,6-dimethoxycarbonyl-1,2,4,5-tetrazine to afford the expected pyridazino-psoralen derivative in good yield. This simple method allowed the efficient preparation of a pyridazino-psoralen derivative with a formyl group at C-7, which was introduced by directed ortho-lithiation in the intermediate 2. An aminoalkyl side-chain was also introduced to the tetracyclic skeleton through the aldehyde functionality in a reductive amination process, which was accompanied by an unprecedented reduction of the pyridazine ring.     

Free radical synthesis of benzofused tricyclic β-lactams by intramolecular cyclization of 2-azetidinone-tethered haloarenes

o-Halogenophenyl- and o-halogenobenzyl-4-alkenyl-β-lactams can be prepared both in the racemic form and in optically pure form using the ketene-imine cyclization. These 2-azetidinone-tethered haloarenes were used for the regio- and stereoselective preparation of benzofused tricyclic β-lactams including benzocarbapenems and benzocarbacephems via intramolecular aryl radical cyclisation.     

A novel and efficient stereo-controlled synthesis of hexahydroquinolinones via the diene-transmissive hetero-Diels-Alder reaction of cross-conjugated azatrienes with ketenes and electrophilic dienophiles

The diene-transmissive hetero-Diels-Alder (DTHDA) reactions of cross-conjugated azatrienes (divinylimines or penta-1,4-dien-3-imines) having an N-aryl, N-alkyl, or N-dimethylamino substituent have been examined. The initial reaction of the azatrienes with diphenylketene at room temperature yielded β-lactams of [2+2] cycloadducts, which upon heating underwent [1,3]-sigmatropic rearrangement to produce the formal [4+2] cycloadducts. The reaction of N-phenylazatriene with dimethylketene or dichloroketene produced the [2+2] cycloadducts only, while the reaction of N-(dimethylamino)azatriene with dichloroketene gave the [4+2] cycloadduct without heating. When the [2+2] cycloadduct has two different vinyl substituents at C-4 of the β-lactam ring, the regioselectivity of the rearrangement depends on steric factors and the electronic demand of the substituents. The second Diels-Alder reaction of the initial [4+2] cycloadducts with electron-deficient dienophiles (TCNE, N-phenylmaleimide) stereoselectively yielded hexahydroquinolinone derivatives. Similarly, a tandem intermolecular-intramolecular mode of the aza-DTHDA reactions produced tetracyclic nitrogen-containing heterocycles in a regio- and stereoselective manner.