A new approach to fused furan ring systems and benzofurans: Intramolecular cyclization reactions of unsaturated acyloxy sulfone derivatives

Unsaturated acyloxy sulfones 3 undergo intramolecular cyclization upon deprotonation with LHMDS in THF. Dehydration and double bond isomerization of the products upon exposure to acid, gave the fused ring furans, 4, in good yields. This strategy could be readily adapted to prepare substituted benzofurans 12 from the cyclization reactions of acyloxy sulfones 11 prepared from phenols. Finally, this approach could be successfully modified to access dihydropyrans and benzopyrans.     

A novel synthetic approach to the ecdysone side chain via furan derivatives

A New type of synthesis of (22R)-22,25-dihydroxycholesterol and its 22S isomer from pregnenolone by using furan derivatives is reported.     

A novel approach to the synthesis of diaza-bridged heterocycle derivatives

A novel synthetic route of diaza-bridged heterocycles based on natural 3,9-diazabicyclo[3.3.1]non-6-ene scaffold has been accomplished. The synthetic approach consists of a Pictet-Spengler condensation of the l-Dopa-OMe with an appropriate aldehyde, Fmoc-Aa-H, followed by intramolecular lactamization. This approach generated two configurationally distinct products (cis and trans-isomers), increasing the stereochemical diversity of these compounds. The synthesized compounds are potentially useful in the discovery of novel pharmacologically active compounds.     

The ‘inverse electron-demand’ Diels-Alder reaction in polymer synthesis. Part 5: Preparation and model reactions of some electron-rich bis-dienamines

The m- and p-phenylene-bridged bis-azolopyridinium salts have been synthesized and converted into the corresponding bis-dienamines by reaction with pyrrolidine. These dienamines react readily with dimethyl 1,2,4,5-tetrazine-dicarboxylate to yield the bis-azolylvinyl-pyridazines.     

Photosensitized intramolecular cyclization of furan and non-activated alkene: pathway switching by the substituent on the furan ring

A photosensitized reaction of furan with a non-activated simple alkene was investigated. Intramolecular Diels-Alder-type cycloaddition reactions between furan and a trisubstituted alkene were found to proceed in high yield in the presence of 9,10-dicyanoanthracene under UV irradiation to afford oxabicyclo[2.2.1]heptane derivatives in high stereoselectivity when the furan was alkyl substituted. On the other hand, the aryl-substituted furan cyclized via a completely different pathway to give spirocyclic and tricyclic products.     

A novel approach to the Taxol A-ring synthetic equivalents

A novel short approach to the A-ring synthetic equivalents of Taxol was described. Oxabicyclic ketone 3 served as a versatile template for selective functionalization leading to oxabicyclic vinylic ether 6 in two steps, which was hydrolyzed under mild acidic conditions to afford the hydroxy aldehyde derivative 7. Synthetic equivalents 2 of Taxol A-ring were thus, accessible from hydroxy aldehyde 7.     

Stereoselective ring expansion via bicyclooxonium ion. A novel approach to oxocanes

[reaction: see text] The stereoselective 1,4-rearrangement-ring expansion of tetrahydrofurans via bicyclo[3.3.0]oxonium ions was developed to synthesize oxocanes. On the basis of this rearrangement, the stereoselective synthesis of 2,8-syn-2,8-dimethyloxocane was accomplished.     

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.     

A novel photochemical Wittig reaction for the synthesis of 2-aryl/alkylbenzofurans

The synthesis of 2-aryl/alkylbenzofurans has been achieved in high yields under photochemical conditions from readily accessible and suitably substituted phosphonium bromides by an intramolecular photochemical Wittig reaction onto aryloxycarbonyl groups.     

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.     

一种合成2-苄基类取代Pyrrolizidine和Pyrrolizidinone环系的新途径

本文报道合成Pyrrolizidinone和Pyrrolizidine环系的新方法,即通过酰亚胺正离子成环,然后经碳正离子重排而成Pyrrolizidinone环系.采用这种方法,合成了六个新的Pyrrolizidinone及Pyrrolizidine生物碱类似物.     

A Diels-Alder approach for the synthesis of highly functionalized benzo-annulated indane-based α-amino acid derivatives via a sultine intermediate

The synthesis of various highly functionalized benzo-annulated indane-based α-amino acid (AAA) derivatives are reported via a [4+2] cycloaddition strategy using a sultine derivative, containing an AAA moiety, as a reactive diene component. By adopting this strategy, a new α,α-dialkylated indane-based C₆₀ fullerene containing a constrained AAA unit is reported.     

An approach to the synthesis of furanoheliangolides through Diels-Alder reactions

The core structure of the natural sesquiterpene lactones furanoheliangolides, an 11-oxabicyclo[6.2.1]undecane system, was synthesized through a pathway involving two Diels-Alder reactions.     

Stereoselective synthesis of the cis-275B decahydroquinoline ring system

The Diels-Alder precursor was constructed from readily available d-glutamic acid utilizing a series of functional group transformations. The stereocenter of the amino acid provided the desired stereochemistry at C2 and diastereoselectively directed the intramolecular Diels-Alder cyclization. This simultaneously generated the three remaining stereocenters and yielded a bicyclic intermediate with all four stereocenters of the target decahydroquinoline 275B.     

A tandem enyne/ring closing metathesis approach to the synthesis of novel angularly fused dioxa-triquinanes

Triquinanes and their oxygenated congeners, oxa- and dioxa-triquinanes, exhibit versatile biological activities in conjunction with synthetically challenging molecular architecture. Owing to these properties, several new strategies have been developed to accomplish the synthesis of these sesquiterpenes. Among the new strategies, cascade radical cyclization strategy has been broadly explored and well studied. Herein, we report our efforts in detail for the synthesis of dioxa-triquinanes using a domino enyne/RCM strategy as the key step. Carbohydrate based synthesis not only allows the use of inexpensive and optically pure starting materials, but also the furanose derivatives, which already possess one of the requisite dihydro-furan moieties in the desired dioxa-triquinane. The other two five-membered rings were constructed simultaneously by the cascade enyne/RCM reaction using the Grubbs' second-generation catalyst. During the course of our synthesis it was observed that the acetonide protection hinders the RCM reaction, after the initial enyne metathesis reaction. The reaction underwent smoothly under argon atmosphere, whilst use of ethylene atmosphere was found to hinder the formation of the tandem enyne/RCM product. The effect of substitution on the key reaction is described here.     

Tandem catalysis in ionic liquids: a recyclable catalytic synthesis of benzofuran derivatives

A convenient, recyclable catalytic synthesis of benzofuran-2-acetic esters 2 by sequential Pd(0)-catalyzed deallylation—Pd(II)-catalyzed carbonylative heterocyclization of 1-(2-allyloxyphenyl)-2-yn-1-ols 1 in ionic liquids is presented. Reactions were typically carried out in BmimBF₄ as the solvent at 100 °C and under 30 atm of CO, in the presence of catalytic amounts (1 mol %) of PdI₂ in conjunction with KI (1 equiv), PPh₃ (4 mol %), MeOH (28 equiv), and H₂O (2 equiv). The solvent-catalyst system could be recycled several times without appreciable loss of catalytic activity.     

A novel approach to synthesis of the cinnoline ring system via organoiron(cyclopentadienyl) complexes

An efficient synthesis of 3-mono or 3,4-disubstituted cinnolines from (o-dichlorobenzene)(cyclopentadienyl)iron hexafluorophosphate in three or four steps has been achieved. o-Chlorophenyl-alkyl or alkylaryl ketone complexes obtained from the o-dichlorobenzene complex upon treatment with enolate anions, react with hydrazine forming 3-mono or 3,4-disubstituted 1,4-dihydrocinnoline complexes. Treatment of the later with sodium amide leads to an aromatization-demetallation reaction resulting in formation of cinnolines, i.e. 3-methyl-, 3-phenyl- and 3,4-dimethylcinnoline. The influence of substituents bonded to the carbon atom adjacent to the complexed benzene ring in o-chlorophenyl -alkyl or -alkylaryl ketone prior to cyclization on the cyclization reaction is discussed.     

A novel approach to the synthesis of benzoic and cinnamic acid derivatives with nor-isoprenoid substituents

A novel strategy for the synthesis of 4-(nor-polyprenyl)-substituted benzoic acids and their esters of the general formula1 as well as their vinylogs of the type2, based on the use of terephthalic aldehyde (3) and its tetramethyl acetal (13), is elaborated. The carbonyl groups in dialdehydes3 and12 can be selectively involved in the reaction sequences leading to the introduction of both aliphatic and functional substituents in positions 1 and 4 of the benzene ring.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 910–913, May, 1993.