Regioselective synthesis of the tricyclic core of lateriflorone

An efficient synthetic approach to the tricyclic core 8 of lateriflorone is described. Essential to the synthesis was the implementation of a biomimetic tandem Claisen/Diels-Alder reaction that produced the desired tricyclic scaffold as a single isomer. A rationalization of the excellent regio and stereoselectivity of this transformation is also proposed. [reaction: see text]     

Asymmetric synthesis of the tricyclic core of cyathin diterpenoids via intramolecular Heck reaction

The enantioselective synthesis of the ketones 3 which displays the carbon core of NGF-inducing cyathane diterpenes is described. The key tricyclic trienone 22 was assembled in 13 steps from Michael adduct (R)-8a via intramolecular Heck cyclization of the chiral triflate 21. The trienone 22 was further elaborated into ketone 3 through trimethylaluminum-promoted expansion of the C-ring with trimethylsilyldiazomethane.     

Synthesis of the tricyclic core of vinigrol via an intramolecular Diels-Alder reaction

[reaction: see text] Herein, we present a successful synthesis of the tricyclic core of vinigrol (1). Our approach takes advantage of a highly regioselective intramolecular Diels-Alder reaction of the diene 11 to construct two rings of the tricyclic vinigrol skeleton 12.     

Stereoselective intramolecular cycloadditions of homochiral N-alkenoyl aryl azides

Starting from the commercially available (S)-1-phenylethylamine and l-alanine benzylester, we synthesised the homochiral N-alkenoyl aryl azides 2a–2d. The intramolecular cycloaddition of unsubstituted 2a and 2b gave enantiopure 3,3a-dihydro-1,2,3-triazolo[1,5-a][1,4]benzodiazepine-4(6H)-ones 3a, 3b, 4a and 4b, while phenyl-substituted 2c and 2d gave enantiopure 1,1a-dihydro-2H-azirino[2,1-c][1,4]benzodiazepine-4(6H)-ones 5c, 5d, 6c and 6d.     

Regioselective synthesis of gentisyl alcohol-type marine natural products

Gentisyl alcohol-type natural products, possessing various important biological properties, have been synthesized from 4-methoxyphenol by using a selective phenol monohydroxymethylation/monochlorination, a CAN oxidation and a sodium dithionite reduction as the key steps. The natural product synthesis is efficient, atom- and step-economical, and requires no protecting groups.     

Asymmetric synthesis of tricyclic tetralin derivatives via an intramolecular photoreaction

An intramolecular photoreaction for the synthesis of tricyclic tetralin derivatives through a Norrish/Yang type cyclization is described. Asymmetric studies on this reaction using ionic chiral auxiliaries gave enantiomeric excesses of up to 99% at conversions of 80%, and the reaction mechanism was mapped out by a single crystal-to-single crystal reaction.     

A strategy for the synthesis of the fargenone/fargenin family of natural products: synthesis of the tricyclic core

A synthesis of the core ring structure of the fargenin/fargenone family of natural products is presented. The general strategy is based upon biosynthetic speculation and exploits a cascade reaction, which transforms a spirocyclic dienone into the core ring system via a deprotonation-oxy-Michael-Wittig olefination sequence. This study represents the first synthesis work towards this family of natural products.     

Stereoselective synthesis of highly functionalised tricyclic β-lactams via intramolecular nitrilimine cycloaddition

The novel azeto[2′,1′:1,2]pyrrolo[3,4-c]pyrazole skeleton has been obtained in both racemic and enantiopure forms by means of intramolecular cycloaddition of nitrilimines 6. Fully stereoselective cycloadditions were obtained, giving tricyclic β-lactams 7 as single diastereoisomers with good overall yields.     

Oppolzer-type intramolecular Diels-Alder cycloadditions via isomerizations of allenamides

A new approach to Oppolzer's intramolecular Diels-Alder cycloaddition (IMDA) through γ-isomerization of readily available N-tethered allenamides is described. These IMDA reactions are carried out in tandem with the allenamide isomerization or 1,3-H shift, leading to complex nitrogen heterocycles in a highly stereoselective manner.     

Total synthesis of flocoumafen via knoevenagel condensation and intramolecular ring cyclization: general access to natural products

The total synthesis and structure determination of cis- and trans-flocoumafen was described. The key synthetic steps involve Knoevenagel condensation with p-methoxybenzaldehyde, in situ decarboxylation and intramolecular ring cyclization to construct the tetralone skeleton. Stereospecific reduction of the O-alkylated ketone 13 afforded good yield of precusor alcohol 5. Final coupling of alcohol 5 with 4-hydroxy-coumarin yielded flocoumafen (1). Separation and structure determination of cis- and trans-flocoumafen through 2D NMR analyses-assisted computer simulation techniques for the evaluation of anticoagulant activities are reported for the first time. This method is useful for generating the core tetralone skeleton of 4-hydroxycoumarin derivatives and provides a generalized access to various warfarin type anticoagulants.     

C-Aryl glycosides via tandem intramolecular benzyne-furan cycloadditions. Total synthesis of vineomycinone B2 methyl ester

A triply convergent total synthesis of vineomycinone B2 methyl ester has been achieved by an approach with a longest linear sequence of 16 steps. The synthesis features the use of silicon tethers as disposable linkers to control the regiochemistry in two tandem Diels-Alder reactions of substituted benzynes and glycosyl furans to provide rapid access to the fully intact anthrarufin core of vineomycinone B2 methyl ester.     

Solid-phase based synthesis of jasplakinolide analogs by intramolecular azide-alkyne cycloadditions

The synthesis of a focused library of jasplakinolide analogs with a 1,2,3-triazole in place of an E-configured double bond is described, featuring the Cu(I) catalyzed azide-alkyne cycloaddition reaction as an efficient macrocyclization tool.     

Intramolecular Diels-Alder reaction leading to tricyclic derivatives as intermediates of natural products synthesis

Tricyclic compounds 4a and 4b possessing a bicyclo[4.3.0] moiety, were successfully synthesized by using the intramolecular Diels-Alder reaction. The siloxy- rather than acyloxy-substituents increased the ratio of the endo-cylcoadducts 10 and 12. The oxygen substitution of 9 influenced conformation of the transition state, which was stereochemically restricted by the butenolide moiety. In addition, 9b carrying a hydroxyl group also produced 10b in a similar ratio to 9a. Compound 11 was the only exo-adduct produced in all of the entries.     

Concise synthesis of the tricyclic core of lycoposerramine S

The tricyclic core of lycoposerramine S has been synthesised in 10 steps from a symmetrical cyclohexadiene precursor by way of a desymmetrising free-radical cyclisation and iodocyclisation.     

Enantiospecific synthesis of the tricyclic core structure of lippifolianes

An enantiospecific synthesis of the [6.6.3]-tricyclic carbon framework, 2,6,6,9-tetra-methyltricyclo[5.4.0.0^2,4]undecane, present in the sesquiterpenes lippifolianes and the diterpenes cyclosclareol, metasequoic acids and parguerols, starting from the readily available monoterpene (R)-carvone, is described.     

Synthetic studies toward GKK1032s, novel antibiotic antitumor agents: enantioselective synthesis of the fully elaborated tricyclic core via an intramolecular Diels-Alder cycloaddition

An enantioselective synthesis of the fully elaborated tricyclic decahydrofluorene core (ABC-ring system) of GKK1032s, novel antimicrobial and antitumor agents, has been accomplished for the first time by employing a highly diastereoselective intramolecular Diels-Alder (IMDA) reaction. The key substrate for the IMDA reaction was efficiently prepared through (i) an intermolecular Diels-Alder reaction between a siloxydiene and an optically active enone derived from D-mannitol to construct the appropriately functionalized C-ring and (ii) CuCl-promoted Stille coupling of an (E)-vinyl iodide and a vinylstannane to install the requisite triene side chain as the crucial steps.     

An intramolecular one-pot synthesis of steroidal triazoles via 1,3-dipolar cycloadditions of in situ generated diazo compounds

A novel synthetic route is reported for the preparation of steroidal triazoles via intramolecular 1,3-dipolar cycloaddition of a steroidal 16,17-seco-17-diazo-16-nitrile system. The structures of the products are established by X-ray and NMR studies. The in vitro antiproliferative activity of the steroidal triazoles against three tumor cell lines was evaluated.     

Application of an intramolecular dipolar cycloaddition to an asymmetric synthesis of the fully oxygenated tricyclic core of the stemofoline alkaloids

An intramolecular non-stabilized azomethine ylide dipolar cycloaddition was applied toward the first non-racemic synthesis of the fully oxygenated bridged pyrrolizidine core (45) of (+)-stemofoline (1) in 11 steps from a commercially available starting material.     

Regioselective synthesis of heterocyclic scaffold by aryl radical cyclization

Regioselective synthesis of a number of coumarin‐annulated pentacyclic heterocycles have been achieved by tri‐n‐butyltin hydride‐mediated aryl radical cyclization. The products are formed as a mixture of cis‐ and trans‐ forms which were successfully separated by careful silica gel flash chromatography.