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An efficient approach for the synthesis of biologically interesting unnatural amino-acids containing 3-hydrooxindole skeleton has been developed. The strategy features a catalyst-free, one-pot, three-component process involving the formation of two new quaternary centers in high yields and with a broad substrate scope.

The first biomimetic synthesis of methyl (8 S ,9 R ,13 R ,14 R )-4,4,8,9,13-pentamethyl-20(10 → 9)-abeo- ent -isocopal-5(10),11(12)-dien-15-oate—a diterpenoid with the ent -verrucosin A/B skeleton has been performed by electrophilic isomerization of methyl 12α-hydroxy- ent -isocopal-13(16)-en-15-oate. The structure and stereochemistry of the synthesized compound have been established on the basis of spectroscopic data.

A five-step synthesis of the 6-6-6 tricyclic skeleton of the diterpene wickerol A is described. The synthesis features a diastereoselective d-proline-mediated Robinson annulation and N-heterocyclic carbene-catalyzed Stetter reaction as key transformations to give the tricyclic carbon skeleton of this promising anti-influenza A natural product.

The 9,10- syn – trans -decalin skeleton has been constructed from (+)-sclareolide via semipinacol rearrangement as a key step. Subsequent divergent transformation of a pivotal intermediate culminated in asymmetric synthesis of (+)- syn -copalol and one analog of immunosuppressive agent candelalide. This synthetic strategy constitutes a good starting point for generating a panel of biologically active natural products.

This Letter describes a highly diastereoselective synthesis of the unique 1-hydroxy endo,endo-2,6-diaryl-3,7-dioxabicyclo[3.3.0]octane skeleton starting from a stereodefined 4-arylidenetetrahydrofuran obtained by a multicomponent reaction. The key step of this synthesis is a dealkylative cyclization reaction performed on the corresponding epoxide, generating four contiguous stereogenic centers with total stereocontrol.

A synthetic study of the Stemona alkaloid stemonamide is described. The FeCl3-promoted fast Nazarov reaction of β-alkoxy divinyl ketones in the presence of t-BuOH afforded an α-methylene cyclopentenone, which was subsequently subjected to the Rh-catalyzed C–H amination to provide a fully appropriately substituted α-methylene cyclopentenone as the core skeleton of stemonamide.

A new, general route to the 1,2-diaryl-substituted pyrrolo[2,1-a]isoquinolines has been developed via the 1,5-dipolar electrocyclisation reactions of azomethine ylides derived from readily available stilbenic acid derivatives. This method was applied to the concise construction of a lamellarin skeleton.

The stepwise oxidative coupling reaction from (S,S)-1 gave optically active oligomers, (S,R,R,S)-2 and (S,R,S,R,R,S,R,S)-3 , having four and eight chiral phosphorus atoms, respectively. The behaviors of these oligomers in the solid state and in solution were investigated in detail. The first construction of a 12-phosphacrown-4 skeleton was also reported.

Compound 4 which represents the skeleton of trigonoliimines A and B was readily obtained in six steps from N-phthaloyl tryptamine, the synthetic strategy employed here was versatile and flexible which also led to a novel bistryptamine framework.

Baruol (1) and Leonal (2), first examples of tetracyclic triterpenes possessing a D:B-friedobaccharane skeleton, were isolated from Maytenus blepharodes and M. chiapensis, respectively. Their structures were established by spectroscopic analysis, molecular modeling studies and biogenetic background. The implication of the D:B-friedobaccharenyl cation in the biosynthetic route of baccharane and shionane skeletons is discussed. Baruol exhibited β-glucuronidase inhibitory activity, a target in the search for hepatoprotective agents.

The annulation of 2-(nitromethyl)benzoates with enones gave 4-nitro-1-naphthols in good yields. The carbocyclic framework of the stealthins was synthesized.

The synthetic approach to a functionalized hydrochrysene skeleton is described. The route is highlighted by a Birch reduction–alkylation sequence and a 6-exo-trig radical cyclization.

4 pages, 2 figures, 1 table, 1 scheme.-- Printed version published Sep 2, 2002., A unique diterpene 1, was isolated from the altiplane Andean plant Azorella madreporica Clos (Apiaceae). The structure and stereochemistry were established by spectral methods and molecular mechanics calculations. The compound possesses a novel hydrocarbon skeleton for which we suggest the name madreporane., The structure and stereochemistry for madreporanone are described., This work was supported by the Ministerio de Ciencia y Tecnología (MCYT, Spain), FEDER (EU), FONDECYT: 1011068 (Chile), Subdirección General de Cooperación Internacional, Program of Cooperation between the Consejo Superior de Investigaciones Científicas (CSIC, Spain) and CONICYT (Chile), and DI of the Universidad de Antofagasta.

The spirolactone core of napalilactone and pathylactone A was synthesized in five steps from 2-methyl-2-cyclohexen-1-one or 2,3-dimethyl-2-cyclohexen-1-one. This spirolactone contains all of the carbon atoms and three of the four stereocenters of napalilactone and pathylactone A.

A general and efficient approach for the synthesis of a kind of dihydrofuran sesquiterpenes extensively present in the Celastraceae family of plants has been developed by a series of transformations from santonin. The key creative and versatile steps involve the strategic acid-catalyzed double-bond shifting affording 6 , the novel base-promoted epoxide rearrangement of 7 generating two key functions (the C5OH and the Δ 7,11 double bond) and the stereoselective construction of a tetrahydrofuran moiety without particularly controlling the stereochemistry of C7. In particular, this approach can introduce any number of hydroxyls at the required positions for synthesis of many natural dihydroagarofuran sesquiterpenes.

On basis of biomimetic concepts, the skeleton of trigonoliimine C was readily achieved in five steps from N-phthaloyl tryptamine. This result suggested a useful synthetic strategy for trigonoliimine alkaloids with this unique ring system.

A novel compound, named salviskinone A (1), was isolated from Salvia przewarskii. The compound has a rearranged carbon skeleton with a methyl unit at C-5 from abietane-type diterpene. Its structure and relative stereochemistry were elucidated by detailed spectroscopic analysis, including HREIMS and 2DNMR (COSY, HSQC, HMBC, and NOESY) spectra. (C) 2011 Elsevier Ltd. All rights reserved.

A new strategy for the synthesis of (+)-vernolepin (1), (+)-vernodalin (2), and (+)-8-deoxyvernolepin (3), from the accessible germacrolides (+)-salonitenolide (4) and (+)-costunolide (5), has been developed. The key steps in the synthesis are a Cope rearrangement from the germacradiene to the elemadiene skeleton, the cyclization of a trans-fused d-lactone from an epoxy ester, and an unusual sulfene elimination, which promotes a reaction cascade leading to the 2-oxa-cis-decalin skeleton. © 2000 Elsevier Science Ltd. All rights reserved.

The photolysis of [3 3 ](1,3,5)cyclophane 8 in MeOH:2N HCl (17:1 v/v) afforded new polycyclic caged dimethoxy and methoxy–hydroxy compounds 12 and 13 with a novel pentacyclo[6.4.0.0 3,7 .0 4,11 .0 5,10 ]dodecane skeleton 7 , in addition to methyl ether 9c with the previously reported skeleton 6 . The unique structural features of 12 and 13 were elucidated by X-ray structural analysis.

A new route to the synthesis of an optically active illudane skeleton from ( R )-(−)-pantolactone ( 4 ) is established. The tricyclic ring system was constructed by Michael–Michael-elimination reaction of the enolate of (3 S ,5 R )-3-( tert -butyldimethylsilyloxy)-5-methoxymethyloxy-1-propionylcyclopentene ( 10 ) with ethyl cyclopropylidenacetate ( 3 ).

The ring system of the novel indole alkaloid tangutorine (1) has been synthesized via the Fry reaction. The final key steps were an oxidation/reduction procedure or alternatively, an epimerization sequence. Conformational and stereochemical aspects of the skeleton are discussed.

The structures of sampsoniones CH, isolated from the aerial parts of Hypericum sampsonii , have been elucidated by extensive analysis of 2 D NMR. Sampsoniones CH are the first polyprenylated benzophenone derivatives with a unique caged tetracyclo[7.3.1.1 3,11 .0 3,7 ]tetradecane-2,12,14-trione skeleton.

Cochinchistemonine (1), an alkaloid with a novel skeleton, was isolated from the roots of Stemona cochinchinensis collected from northern Vietnam. Its structure was established on the basis of one- and two-dimensional NMR and other spectroscopic studies. The relative configuration was confirmed by single crystal X-ray diffraction experiment.

Fully functionalized decalin skeleton of (+)-fusarisetin A is stereoselectively synthesized from (+)-citronellal and methyl ( S )-(+)-3-hydroxybutyrate. The bicyclic framework has been constructed using intramolecular Diels–Alder reaction.

A concise, novel route to the geissoschizine skeleton has been developed. The key step involves a Heck cyclization reaction, which was found to lead to opposite diastereomers, (±)- 8 or (±)- 9 , depending on the reaction conditions.

Tricyclic trinervitane and tetracyclic kempane skeletons are constructed from the common intermediate possessing bicyclic secotrinervitane skeleton on the basis of biogenetical consideration.

The Pauson-Khand reaction of the (3S,4S)-3,4-bis(tert-butyldimethylsilyloxy)-7-octen-1-yne derivatives, derived from (+)-diethyl tartrate, exclusively gave the (2S,3S,6S)-2,3-bis(tert-butyldimethylsilyloxy)bicyclo[4.3.0]non-1(9)-en-8-one derivatives, while the (3S,4S)-3,4-dihydroxy-7-octen-1-yne congeners diastereocomplementarily afforded the corresponding (2S,3S,6R)-2,3-dihydroxy-bicyclo[4.3.0]non-1(9)-en-8-one in a highly selective manner.

A related synthetic strategy has been used to prepare two natural products (XH-14 and ailanthoidol) which possess a benzo[ b ]furan skeleton. The synthesis of XH-14 involved the use of a palladium-catalyzed cyclization with concomitant carbonylation via insertion of carbon monoxide to introduce regioselectively a formyl group in the 3-position.

The first synthesis of the benzannelated spiroketal core of γ-rubromycin using Henry condensations and a novel Nef-type reaction induced by Pearlman's catalyst is described.

Erythrolide K (4), isolated from Erythropodium caribaeorum possesses an unusual bicyclo [9.2.1.] tetradecane skeleton. The structure was deduced by 2D NMR and confirmed by X-ray analysis. It was synthesised in two steps from erythrolide A (2), the first involving a thermal [1,5] sigmatropic hydrogen shift to give the intermediate (3).

The aerial parts of Nauplius graveolens subsp. odorus ( Schousb ) Wikl. afforded a novel sesquiterpene lactone ( 1 ) named naupliolide together with the known 6,7,9,10-tetradehydroasteriscanolide 2 and asteriscunolides A–D 3a – d . The structure of compound 1 corresponds to a novel skeleton of 14,15-dimethyl-7,13-dioxotricyclic[6.4.0.0 9,11 ]dodeca-12,13-olide, and was established on the basis of spectroscopic methods including 2D-NMR. The coexistence of naupliolide 1 together with the structurally related sesquiterpene lactones asterisculolides A–D ( 3a – d ) and 6,7,9,10-tetradehydroasteriscanolide 2 , seems to indicate their biosynthetic relationship.

A novel and general approach has been delineated for the enantiomerically pure synthesis of the angularly fused tricyclic system of the pentalenolactone family of compounds. D-Glucose is used as starting material and a diasteroselective Diels-Alder reaction sets the elements for the ring junctions.

Irradiations of 2-(1-naphthyl)ethyl 3-anilinoalkanoates ( 3a-c ) in degassed benzene afforded tricyclic lactones ( 4a-c ) containing 2-azabicyclo[3.3.1]nonane skeleton as major products via photo-induced electron transfer.

Several 2-(2-phenylethyl)chromones have been shown to possess neuroprotective activity. However, limited synthetic methods have been disclosed to construct the 2-(2-phenylethyl)chromone skeleton. Herein, we report a straightforward 3-step preparation of five naturally occurring 2-(2-phenylethyl)chromones utilizing the Claisen condensation as the key step.

Birdcaged bicyclo[2.2.2]octene-1,4-diol 15 was prepared from Diels-Alder adduct of 5,5-dimethoxy-1,2,3,4-tetrachlorocyclopentadiene in five steps. This diol underwent DIB-promoted fragmentation to give tetracyclic dienes 16 and 17 . Intramolecular [2+2]photocyclization of 16 and 17 furnished hexacyclic cage compounds 18 and 19 having homosecohexaprismane skeleton.

Two highly convergent routes to the acetoxyodontoschismenol dolabellane skeleton are described. Both utilise efficient organozirconium based coupling reactions to rapidly assemble macro-cyclisation precursors. The first approach closes the key eleven membered ring of the dolabellane skeleton by an intramolecular Nozaki - Hiyama reaction, whereas the second uses an intramolecular α-sulphonyl carbanion - allyl iodide condensation.

Addition of 2-aminobenzylamine to methyl trifluoropyruvate afforded methyl 2-((2-aminobenzyl)amino)-3,3,3-trifluoro-2-hydroxypropionate, which reacted with various ketones to give new fluorinated tricyclic and tetracyclic heterocycles with the skeleton of the alkaloid Peganin.

A new C23 terpenoid, 13, 14-dioxo-11-hydroxy-7-methoxy-hassane-8, 11, 15-trien-(22,6)-olide 2 was isolated from the aerial part of Salvia apiana Jeps. This new C23 terpenoid has a new basic skeleton 1 for wich we propose the name of hassanane. The structure of 2 was established from its spectroscopic data. A possible common biosynthetic origin of 2 and the previously reported apiananes is also discussed.

Three tricyclic sesquiterpenes, sesquithuriferol ( 1 ), α- ( 3 ) and β-duprezianene ( 4 ) were isolated from the essential oil of the wood of Juniperus thurifera L. The structure and absolute configuration of 1 was established on the basis of 2D INADEQUATE and other 2D NMR spectra, as well as by chemical correlations. The structure of 3 and 4 were elucidated by 2D NMR spectra and confirmed by their synthesis from tosyl-solvolysis rearrangement of 1 .

The synthesis of nonamethylcorilagin is described. In the synthesis, the intramolecular Ullmann coupling afforded the (R)-hexahydroxydiphenoyl part––a characteristic bridge structure of the target molecule––when the glucopyranose ring was opened in advance. This synthesis demonstrates the first synthetic approach to a 3,6-bridged ellagitannin skeleton whose conformation of the d -glucose core is 1C4 or skew boat.

An approach to the hydroazulen skeleton of the tremulane sesquiterpenes by synthesis of the title compound 5 is described.

The RCM metathesis reaction catalyzed by Grubbs’ ruthenium catalyst is used with a series of 1,2-disubstituted indoles leading with excellent yields to tricyclic compounds. When applied to 1-allyl-2-vinylindoles this methodology allows a new entry to the mitosene skeleton.

The synthesis of unique diquinanes, possessing four continuous methyl groups on the convex of the diquinane skeleton, has been achieved by employing a combination of pinacol-type rearrangement and efficient anionic [1,3] rearrangement strategies.

A short synthetic route to 16-demethyleneervitsine ( 6 ), based on the nucleophilic addition of 2-acetylindole enolates to N -alkyl-β-acylpyridinium salts and further acid cyclization of the resulting 1,4-dihydropyridine intermediates, is reported.

An expeditious synthesis of Taxol skeleton is described utilizing the combination of intramolecular Diels-Alder (IMDA) and Wittig rearrangement reactions.

A convergent route to the polyketide sesquiterpene skeleton of robustadial and euglobal is described.

A concise synthesis of the isoindolobenzazepine aporhoeadane core is achieved in four steps from homoveratrylamine and ninhydrin.

A two-directional synthesis strategy and a tandem deprotection/double intramolecular Michael addition provides a very direct route to the 4,6-disubstituted quinolizidine 4.

An efficient total synthesis of 2-pupukeanone is reported which involves a 5-exo-trig allyl radical cyclization as the key step to construct the isotwistane skeleton.

Yonarolide, a new marine norditerpenoid possessing a novel tricyclic skeleton, was isolated from the Okinawan soft coral of the genus, Sinularia. The structure of yonarolide was determined by spectroscopic analysis.