Gold-catalyzed and N-iodosuccinimide-mediated cyclization of gamma-substituted allenamides

Chiral gamma-substituted allenamides have been shown to undergo efficient gold-catalyzed and N-iodosuccinimide-mediated cyclization to highly functionalized dihydrofurans. These reactions proceed rapidly and without loss of stereochemistry.     

Copper-catalyzed stereospecific N-allenylations of amides. Syntheses of optically enriched chiral allenamides

[reaction: see text] Syntheses of chiral allenamides via a stereospecific amidation of optically enriched allenyl iodides using catalytic copper(I) salt and N,N'-dimethylethylene-diamine are described here.     

Syntheses and insecticidal activities of novel 2,5-disubstituted 1,3,4-oxadiazoles

Nine novel symmetrical and asymmetrical 2,5-disubstituted 1,3,4-oxadiazoles have been synthesized by a facile and mild method with high yield. Meantime, it was found that the fluorine was easy substituted by hydrazine in polyhalogen-substituted aroyl hydrazine. The preliminary bioassay tests show that two of the compounds (D5 and D6) exhibited a significant insecticidal activity (LC₅₀=116.02 and 70.93 mg l⁻¹) on armyworm, Leucania separata Walker. Using the Drug Discovery Workbench (DDW) (Cerius²), structure-activities relationship was studied.     

Enantioselective partial reduction of 2,5-disubstituted pyrroles via a chiral protonation approach

[reaction: see text] The partial reduction of 2,5-pyrrole diester 1 followed by enantioselective protonation in situ to furnish synthetically useful building blocks is described. An enantiomeric excess of up to 74% was achieved using (-)-ephedrine and related analogues as chiral proton sources. The pyrroline product obtained could be recrystallized to give enantiomerically pure material.     

Preparation of 2,5-disubstituted oxazoles from N-propargylamides

[reaction: see text] 2,5-Disubstituted oxazoles have been prepared through the reaction of N-propargylamides with aryl iodides in the presence of Pd(2)(dba)(3), tri(2-furyl)phosphine, and NaO(t)()Bu. The reaction appears to proceed through a palladium-catalyzed coupling step followed by the in situ cyclization of the resultant coupling product.     

Partially hydroxylated 2,5-disubstituted bis-tetrahydrofurans from carbohydrates

The diverse bioactivities of annonaceous acetogenins have recently attracted increasing interest. Many of these natural products contain one or more 2,5-disubstituted tetrahydrofuran rings as a core unit; these are important for the bioactivity, since it is believed that these anchor the compounds to the surface of the membrane. Therefore, the synthesis of functionalized bis-tetrahydrofurans is an important task and we have developed a synthetic pathway to all four diastereomeric, partially hydroxylated bis-tetrahydrofurans, that is, 3,6:7,10)-dianhydro-2,8,9-trideoxy-L-erythro-D-ido-undecitol (1), 3,6:7,10-dianhydro-2,8,9-trideoxy-D-threo-D-ido-undecitol (2), 3,6:7,10-dianhydro-2,8,9-trideoxy-L-threo-D-ido-undecitol (3), and 3,6:7,10-dianhydro-2,8,9-trideoxy-D-erythro-D-ido-undecitol (4) starting from D-glucose. The reaction of the aldose with Meldrum's acid led to the C-glycosidic 3,6-anhydro-1,4-lactone 6, which was converted to the aldehyde building block 2,5-anhydro-3,4,7-tri-O-benzyl-6-deoxy-aldehydo-D-ido-heptose (11). Chain elongation of 11 with the Grignard reagent derived from 1-bromo-3-butene gave the diastereomers 3,6-anhydro-1,4,5-tri-O-benzyl-2,8,9,10,11-pentadeoxy-L-glycero-D-ido-undec-10-enitol (12) and 3,6-anhydro-1,4,5-tri-O-benzyl-2,8,9,10,11-pentadeoxy-D-glycero-D-ido-undec-10-enitol (13). The relative threo configuration of the major product 12 was confirmed by X-ray structure analysis. Epoxidation and subsequent cyclization afforded the cis and trans diastereomers 19 and 20, respectively, in a 1:1 ratio. Subsequent cleavage of the protecting groups and separation of the isomers furnished the target compounds in good overall yields.     

A strategy for the synthesis of 2,3-disubstituted indoles starting from N-(o-halophenyl)allenamides

A strategy for the synthesis of 2,3-disubstituted indole derivatives based on an intramolecular carbopalladation-anion capture cascade has been developed, wherein construction of the pyrrole ring and functionalisation of the indole C2 and C3 positions were achieved by extensive use of palladium(0)-catalysed coupling reactions.     

Asymmetric alkylation of carboxyamides by using trans-2,5-disubstituted pyrrolidines as chiral auxiliaries

trans-2,5-Bis(methoxymethyl)- and trans-2,5-bis(methoxymethoxymethyl)pyrrolidines proved to be excellent chiral auxiliaries for the asymmetric alkylation of the corresponding carboxyamide enolates giving good chemical yield and high stereoselectivity (invariably over 95% de), with remarkable flexibility to substrates and reaction conditions.     

Synthesis of 2,5-disubstituted 1,3,4-oxadiazoles from trichloromethylarenes and acylhydrazines

A preparative synthesis of 2,5-disubstituted 1,3,4-oxadiazoles by the reaction of trichloromethylarenes with hydrazides of carboxylic acids of the aliphatic, aromatic and heteroaromatic series in methanol or ethanol in the presence of pyridine was developed.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 117913. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 686–692, May, 1994. Original article submitted April 8, 1994.     

Synthesis of 2,5-disubstituted tetrahydrofurans from organozinc halides and lactones

<正>2,5-Disubstituted tetrahydrofurans were obtained from lactones and organozinc halides in moderate to high yield in the presence of Lewis acids.     

Diastereoselective synthesis of 2,5-disubstituted tetrahydrofurans

This review focuses on synthetic methods allowing the preparation of 2,5-disubstituted tetrahydrofurans reported in the literature between 1993 and 2008.     

Liquid crystalline 2,5-disubstituted pyridine derivatives

This paper presents a review of the work on the molecular design of liquid crystalline 2,5-disubstituted pyridine derivatives for the twisted nematic (TN) and super twisted nematic (STN) liquid crystal displays (LCDs) and examines in some detail the correlations between the molecular structure of pyridine derivatives and their physico-chemical properties.     

Syntheses of functionalized 1,4-disubstituted gamma-carbolines

We report the complete synthesis of a variety of 1,4-disubstituted gamma-carbolines. These compounds are of particular interest for their involvement in many biological processes and are believed to possess various medicinal activities. A large number of N-tosylaldimines were condensed with indoles affording an array of 3-aminomethyl indoles. Subsequent additions, followed by intramolecular cyclization, afforded an array of 1,2-dihydro-3H-gamma-carbolones in good yield. Upon subsequent aromatization, the corresponding fully aromatic functionalized 1-aryl-4-hydroxy-gamma-carbolines resulted.     

Synthesis of chirally pure 2,5-disubstituted diketopiperazines derived from trisubstituted phenylalanines

Some new chirally pure 2,5-substituted diketopiperazines were synthesized starting from 2-methoxybenzyl alcohol. This multistep synthesis proceeds through the enzymatic synthesis of chirally pure amino acids, protection and dipeptide coupling, cyclization of dipeptide ester formates, and nitration of the resulting diketopiperazines.     

Asymmetric homogeneous hydrogenation of 2,5-disubstituted furans

A homogeneous catalyst system for the asymmetric cis-hydrogenation of 2,5-disubstituted furans leading to 2',3'-dideoxynucleoside analogues is described. Best enantioselectivities (ee values of up to 72%) were obtained with cationic rhodium complexes ligated by diphospholanes of the butiphane family. The selectivity of the hydrogenation was reversed by the addition of a base or a polar protic solvent in certain cases. Ferrocene- and proline-based systems gave significant, but lower, ee values.     

由糖合成手性纯天然化合物

简要回顾了15年来作者在糖为手性源合成天然产物,尤其是一系列高生物活性脂链化合物方面所取得的进展,以及其中合成策略和合成方法学方面的一些新结果。     

Access to 2,5-disubstituted tetrahydrofurans from Grignard reagents and hemiacetal derivatives

The first diastereoselective addition of Grignard reagents onto cyclic oxocarbenium ions, obtained from glycosyl acetates, to afford 2,5-disubstituted tetrahydrofurans, is reported.     

Synthesis of 2,5-disubstituted 6-azaindoles from substituted aziridines via intramolecular cyclization

A new and efficient preparation of pharmacologically and biologically important 2,5-disubstituted 6-azaindoles was achieved from cyclizations of aziridin-2-yl dipropargylic alcohols as adducts of two propargyl groups to ethyl 1-benzylaziridine-2-carboxylate. The sequential cyclizations include pyrrole formation and a novel base-catalyzed intramolecular acetylenic Schmidt reaction.     

Gold-catalysed synthesis of amino acid-derived 2,5-disubstituted oxazoles

Amino acid-derived propargylic amides are cyclised in a one-pot, Au(III)-catalysed operation to yield 5-bromomethyl oxazoles. These compounds are further elaborated to bis-heterocycles, dipeptide mimics and more.