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Showing papers on "Intramolecular reaction published in 2004"


Journal ArticleDOI
TL;DR: In this article, the authors used 2-methyl-6-nitrobenzoic anhydride with triethylamine as a basic catalyst for the condensation reaction.
Abstract: Various carboxylic esters are obtained at room temperature in excellent yields with high chemoselectivities from nearly equimolar amounts of carboxylic acids and alcohols using 2-methyl-6-nitrobenzoic anhydride with triethylamine by the promotion of a basic catalyst such as 4-(dimethylamino)pyridine. A variety of lactones are also prepared in high yields at room temperature from the corresponding ω-hydroxycarboxylic acids with use of 2-methyl-6-nitrobenzoic anhydride in the presence of 4-(dimethylamino)pyridine. A similar reaction occurs with triethylamine when using a catalytic amount of 4-(dimethylamino)pyridine 1-oxide as an effective promoter for the intramolecular condensation reaction. These methods are successfully applied to the synthesis of erythro-aleuritic acid lactone and an eight-membered-ring lactone moiety of octalactins A and B. The efficiency of the cyclizations is compared to those of other reported lactonizations.

342 citations


Journal ArticleDOI
TL;DR: A new electron-deficient chiral triazolium salt has been shown to catalyze the formation of quaternary stereocenters by an asymmetric intramolecular Stetter reaction, allowing for functional group relationships that are particularly difficult to access by other methods.
Abstract: A new electron-deficient chiral triazolium salt has been shown to catalyze the formation of quaternary stereocenters by an asymmetric intramolecular Stetter reaction. Pentafluorophenyl substitution on an aminoindanol-derived catalyst affords tertiary ether, thioether, and quaternary stereocenters in typically greater than 90% ee and very good chemical yield. Aromatic and aliphatic aldehydes are equally competent substrates for this reaction. The reaction proceeds at room temperature under mild conditions to provide quaternary stereocenters with functional group relationships that are particularly difficult to access by other methods.

270 citations


Journal ArticleDOI
TL;DR: Direct arylation reactions with improved scope and catalyst activity for the intramolecular formation of biaryl compounds are described through the establishment of a highly active and robust catalyst system and the subsequent development of a novel phosphine ligand.
Abstract: In this Communication, we describe direct arylation reactions with improved scope and catalyst activity for the intramolecular formation of biaryl compounds. This was achieved through the establishment of a highly active and robust catalyst system and the subsequent development of a novel phosphine ligand 27. The enhanced catalytic activity extends these transformations to include previously unreactive and poorly reactive substrates, and allows for very low catalyst loadings to be employed-as little as 0.1 mol %.

240 citations


Journal ArticleDOI
TL;DR: The first highly enantioselective catalytic reaction involving aromatic C-H bond activation is communicated and the identified catalyst system enables the intramolecular alkylation reaction to be performed at temperatures 75 degrees C lower than the previously reported achiral system.
Abstract: The first highly enantioselective catalytic reaction involving aromatic C−H bond activation is communicated. Enantioselective cyclization of aromatic ketimines containing alkenyl groups tethered at the meta position of an imine directing group has been achieved using 5 mol % [RhCl(coe)2]2 and 15 mol % of an (S)-binol-derived phosphoramidite ligand. Selectivities of up to 96% ee and up to quantitative yields were obtained. Moreover, the identified catalyst system enables the intramolecular alkylation reaction to be performed at temperatures 75 °C lower than our previously reported achiral system. The reaction can even be performed at room temperature for one of the optimal substrates.

237 citations


Journal ArticleDOI
TL;DR: In this paper, (S)-alpha-methyl proline catalyzes the intramolecular alkylation of various halo aldehydes to the corresponding formyl cyclopentanes, -cyclopropanes, or -pyrrolidines in excellent yields and enantioselectivities.
Abstract: The development of a general catalytic asymmetric aldehyde alpha-alkylation reaction constitutes a major challenge in organic synthesis. Here, we report the first and successful approach toward its solution: (S)-alpha-methyl proline catalyzes the intramolecular alkylation of various halo aldehydes to the corresponding formyl cyclopentanes, -cyclopropanes, or -pyrrolidines in excellent yields and enantioselectivities. Most remarkably, racemization, aldolization, or catalyst alkylation do not occur to any significant extend, further illustrating the power, mildness, and profound selectivity of enamine catalysis.

213 citations


Journal ArticleDOI
TL;DR: A novel palladium migration methodology for the synthesis of complex fused polycycles has been developed that involves 1,4-palladium alkyl to aryl migrations via through-space C-H activation, followed by intramolecular arylation or an intermolecular Heck reaction providing a very efficient way to synthesize fused ring systems.
Abstract: A novel palladium migration methodology for the synthesis of complex fused polycycles has been developed. This process involves 1,4-palladium alkyl to aryl migrations via through-space C−H activation, followed by intramolecular arylation or an intermolecular Heck reaction providing a very efficient way to synthesize fused ring systems.

201 citations


Journal ArticleDOI
TL;DR: The Pd-catalyzed reaction of internal alkynes with tethered amino groups in the presence of PhCO2H and RENORPHOS as chiral phosphine ligand is reported.
Abstract: The Pd-catalyzed reaction of internal alkynes with tethered amino groups in the presence of PhCO2H and RENORPHOS as chiral phosphine ligand is reported. Various five- and six-membered nitrogen-containing heterocycles were obtained in good to high yield with moderate to high ee.

198 citations


Journal ArticleDOI
TL;DR: This reaction provides not only a useful procedure for synthesizing 2,3-disubstituted indoles at once from ortho-alkynylaniline derivatives, but also an interesting mechanistic aspect; the intramolecular C-N bond addition of amides to alkynes takes place readily in the presence of Pt(II) catalyst.
Abstract: The intramolecular aminoacylation of alkynes using ortho-alkynylacetanilides proceeds in very high yields in the presence of PtCl2 catalyst. This reaction provides not only a useful procedure for synthesizing 2,3-disubstituted indoles at once from ortho-alkynylaniline derivatives, but also an interesting mechanistic aspect; the intramolecular C−N bond addition of amides to alkynes takes place readily in the presence of Pt(II) catalyst.

176 citations


Journal ArticleDOI
TL;DR: In this paper, the catalytic reaction of 1-methy-2-(4-pentenyl)indole with a catalytic amount of PtCl2 in dioxane that contained a trace of HCl (5 mol %) at 60 °C for 24 h led to the isolation of 4,9-dimethyl-2,3,4,9tetrahydro-1H-carbazole (2) in 92% yield.
Abstract: Reaction of 1-methy-2-(4-pentenyl)indole (1) with a catalytic amount of PtCl2 (2 mol %) in dioxane that contained a trace of HCl (5 mol %) at 60 °C for 24 h led to the isolation of 4,9-dimethyl-2,3,4,9-tetrahydro-1H-carbazole (2) in 92% yield. Platinum-catalyzed cyclization of 2-(4-pentenyl)indoles tolerated substitution at each position of the 4-pentenyl chain. Furthermore, the protocol was applicable to the synthesis of tetrahydro-β-carbolinones and was effective for cyclization of unprotected indoles. 2-(3-Butenyl)indoles underwent platinum-catalyzed cyclization with exclusive 6-endo-trig regioselectivity. Mechanistic studies established a mechanism for the platinum-catalyzed cyclization of 2-alkenyl indoles involving nucleophilic attack of the indole on a platinum-complexed olefin.

156 citations


Journal ArticleDOI
TL;DR: Complex [Ru(F(20)-TPP)(CO)] is an active catalyst for intramolecular aziridination of unsaturated sulfonamides with PhI(OAc)(2), producing corresponding bicyclic azirids in up to 87% yield with up to 100% substrate conversion and high turnover
Abstract: Ruthenium porphyrins [Ru(F20-TPP)(CO)] (F20-TPP = 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato dianion) and [Ru(Por*)(CO)] (Por* = 5,10,15,20-tetrakis[(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracen-9-yl]porphyrinato dianion) catalyzed intramolecular amidation of sulfamate esters p-X-C6H4(CH2)2OSO2NH2 (X = Cl, Me, MeO), XC6H4(CH2)3OSO2NH2 (X = p-F, p-MeO, m-MeO), and Ar(CH2)2OSO2NH2 (Ar = naphthalen-1-yl, naphthalen-2-yl) with PhI(OAc)2 to afford the corresponding cyclic sulfamidates in up to 89% yield with up to 100% substrate conversion; up to 88% ee was attained in the asymmetric intramolecular amidation catalyzed by [Ru(Por*)(CO)]. Reaction of [Ru(F20-TPP)(CO)] with PhINSO2OCH2CCl3 (prepared by treating the sulfamate ester Cl3CCH2OSO2NH2 with PhI(OAc)2) afforded a bis(imido)ruthenium(VI) porphyrin, [RuVI(F20-TPP)(NSO2OCH2CCl3)2], in 60% yield. A mechanism involving reactive imido ruthenium porphyrin intermediate was proposed for the ruthenium porphyrin-catalyzed intramolecular...

148 citations


Journal ArticleDOI
TL;DR: Methods for the synthesis of dihydroazaphenanthrene fused to macrocycles and medium-ring heterocycles, as well as 1,4-benzodiazepine-2,5-diones, are developed to develop a divergent synthesis of two different heterocyclic scaffolds from the same starting materials.
Abstract: Methods for the synthesis of dihydroazaphenanthrene fused to macrocycles (2) and medium-ring heterocycles (4), as well as 1,4-benzodiazepine-2,5-diones (5), are developed. A distinctly different catalytic property of palladium and copper catalysts was uncovered that leads to the development of a divergent synthesis of two different heterocyclic scaffolds from the same starting materials, simply by metal-switching. Thus, starting from linear amide 3, palladium acetate triggers a domino intramolecular N-arylation/C−H activation/aryl−aryl bond-forming process to provide 4, while copper iodide promotes only the intramolecular N-arylation reaction leading to 5. In combination with the Ugi multicomponent reaction (Ugi-4CR) for the preparation of the linear amides, a two-step synthesis of either the 5,6-dihydro-8H-5,7a-diazacyclohepta[jk]phenanthrene-4,7-dione (4) or 1,4-benzodiazepine-2,5-diones (5), by appropriate choice of metal catalyst, is subsequently developed from very simple starting materials.

Journal ArticleDOI
TL;DR: A gold-catalyzed cyclialkylation of electron-rich arenes with tethered epoxides afforded 3-chromanols stereospecifically.
Abstract: A gold-catalyzed cyclialkylation of electron-rich arenes with tethered epoxides afforded 3-chromanols stereospecifically.

Journal ArticleDOI
TL;DR: The expected aziridine was not observed, but rather simultaneous spirocyclization of C(3) and stereoselective syn-acylation at C(2) occurred to give compound 41, whose structure was unequivocally established by an X-ray crystallographic study.
Abstract: Several unsaturated sulfonamides underwent intramolecular aziridination when treated with PhI(OAc)(2), MgO, and catalytic Rh(2)(OAc)(4) to give bicyclic aziridines in excellent yield. Treatment of the resulting azabicyclic sulfonamides in methanol in the presence of p-TsOH resulted in exclusive opening of the aziridine ring at the most substituted position affording six- and seven-membered ring products in high yield. In contrast, the intramolecular aziridination of several cycloalkenyl-substituted carbamates did not require a Rh(II) catalyst and proceeded via an iminoiodinane intermediate. The resulting tricyclic aziridines underwent ring opening when treated with various nucleophiles to give anti-derived products as expected for nucleophilic attack at the three-membered ring. The iodine(III)-mediated reaction of a 3-indolyl-substituted carbamate, however, required a Rh(II) catalyst. The expected aziridine was not observed, but rather simultaneous spirocyclization of C(3) and stereoselective syn-acylation at C(2) occurred to give compound 41, whose structure was unequivocally established by an X-ray crystallographic study. The reaction proceeds in a stepwise manner via a metal-free zwitterionic intermediate which is attacked by a nucleophilic reagent on the same side of the amide anion. Related reactions occurred with both a 2-indolyl- and 3-benzofuranyl-substituted carbamate but with lower stereoselectivity.

Journal ArticleDOI
TL;DR: The convergent total synthesis of brevetoxin B has been achieved and the intramolecular allylation of the O,S-acetal 20, prepared from the alpha-chlorosulfide 17 and the alcohol 5, was carried out using AgOTf as a Lewis acid to give the diene 21.
Abstract: Brevetoxin-B (BTX-B), produced by the red tide organism, Gymnodium breve Davis, is the first member of marine polycyclic ethers to be structurally elucidated and one of the most potent neurotoxins. The structural feature is a trans-fused polycyclic ether ring system with 23 stereocenters. Its unique, complex structure and potent biological activity have attracted the attention of synthetic organic chemists. Total synthesis of BTX-B has been accomplished via the coupling of the ABCDEFG and IJK-ring segments, each ether ring of which was stereoselectively and efficiently constructed on the basis of SmI2-induced intramolecular cyclization, 6-endo-cyclization of hydroxy epoxide, ring-closing olefin metathesis, and SmI2-induced intramolecular Reformatsky-type reaction. Several kinds of double reactions at the left and right sides were efficiently used through the synthesis.

Journal ArticleDOI
TL;DR: The first enantioselective total synthesis of (+)-brasilenyne has been achieved in 19 linear steps, with 5.1% overall yield from l-(S)-malic acid.
Abstract: The first enantioselective total synthesis of (+)-brasilenyne (1) has been achieved in 19 linear steps, with 5.1% overall yield from l-(S)-malic acid. The construction of the oxonin core containing a 1,3-cis,cis diene unit was accomplished with a tandem ring-closing metathesis/silicon-assisted intramolecular cross-coupling reaction. In addition, a key propargylic stereogenic center was created through a novel, highly diastereoselective ring opening of a 1,3-dioxolanone promoted by TiCl4. This reaction proceeded through an oxocarbenium ion intermediate and the asymmetric induction was fully controlled by l-malic acid residue. The C(8) stereogenic center was set by a reagent-controlled asymmetric allylboration.

Journal ArticleDOI
TL;DR: Qualitative yields of 10-hydroxy-10,9-boroxarophenanthrenes were obtained as unexpected major products upon BBr(3)-mediated O-demethylation of 2-methoxybiaryls through Pd-catalyzed CO insertion and Suzuki reaction.
Abstract: 10-Hydroxy-10,9-boroxarophenanthrenes were obtained as unexpected major products upon BBr(3)-mediated O-demethylation of 2-methoxybiaryls. The formation likely proceeds via intramolecular electrophilic aromatic cyclization of a reactive dibromoaryloxyborane intermediate. Essentially quantitative yields of 10-hydroxy-10,9-boroxarophenanthrenes were also obtained from 2-hydroxybiaryl and BCl(3)/AlCl(3) with use of a modified literature procedure. As synthetic intermediates, 10-hydroxy-10,9-boroxarophenanthrenes were efficiently converted to 3,4-benzocoumarins and triaryls through Pd-catalyzed CO insertion and Suzuki reaction.

Journal ArticleDOI
Hiroaki Ohno1, Hisao Hamaguchi1, Miyo Ohata1, Shohei Kosaka1, Tetsuaki Tanaka1 
TL;DR: This is the first example that demonstrates the synthesis of medium-sized rings via cyclization of bromoallenes, and this reaction provides a very useful method for a catalytic synthesis of seven- and eight-membered heterocycles without using high dilution conditions.
Abstract: We have developed a highly regio- and stereoselective synthesis of medium-sized heterocycles containing one or two heteroatoms via cyclization of bromoallenes bearing an oxygen, nitrogen, or carbon nucleophilic functionality in the presence of a palladium(0) catalyst and alcohol. In this reaction, bromoallenes act as an allyl dication equivalent, and the intramolecular nucleophilic attack takes place exclusively at the central carbon atom of the allene moiety. Interestingly, bromoallenes having a carbon nucleophile with a five-atom tether afford eight-membered rings with trans-configuration, while those having an oxygen or a nitrogen nucleophile give the corresponding cis-rings selectively. This is the first example that demonstrates the synthesis of medium-sized rings via cyclization of bromoallenes, and this reaction provides a very useful method for a catalytic synthesis of seven- and eight-membered heterocycles without using high dilution conditions.

Journal ArticleDOI
TL;DR: A metal-free approach to chroman derivatives by the reaction of different allylphenyl ethers with Ipy2BF4 is described, and can be extended to the synthesis of tetrahydroquinolines when using allylamines.
Abstract: A metal-free approach to chroman derivatives by the reaction of different allylphenyl ethers with Ipy2BF4 is described. The access to this frame, by direct cyclization of the starting materials, takes place smoothly. In addition, an unusual and selective sequence that comprises initial rearrangement and further cyclization could be accomplished, with temperature as an excellent element of control. The process can be extended to the synthesis of tetrahydroquinolines when using allylamines. Also, two cascade reactions, leading to relevant oxygen and nitrogen-containing skeletons, have been devised.

Journal ArticleDOI
TL;DR: Experiments revealed that some of the newly synthesized pyridinols are the most effective phenolic chain-breaking antioxidants reported to date.
Abstract: The synthesis and study of a series of 6-substituted-2,4-dimethyl-3-pyridinols having interesting antioxidant properties is reported. The general synthetic strategy leading to the compounds involved a low-temperature aryl bromide-to-alcohol conversion as the last step. 2,4-Dimethyl-3-pyridinol (1a), 2,4,6-trimethyl-3-pyridinol (1b), and 2,4-dimethyl-6-(dimethylamino)-3-pyridinol (1d) were thus prepared from the corresponding 3-bromopyridine precursor. The methoxy derivative 2,4-dimethyl-6-(methoxy)-3-pyridinol (1c) was also prepared by an alternate route via a Baeyer−Villiger reaction on the substituted benzaldehyde precursor. Novel bicyclic pyridinols 2 and 3 required prior construction of the ring structure. Thus, 2 was prepared by the use of a 6-step intramolecular Friedel−Crafts strategy, and 3 required an 11-step sequence with a thermolytic intramolecular inverse-demand Diels−Alder reaction between a pyrimidine ring and an alkyne as the key step. Basicities of the pyridinols approached physiological ...

Journal ArticleDOI
TL;DR: It is demonstrated that relatively short simulations can provide us with several possible reaction mechanisms for the rearrangement of azulene to naphthalene, and that different choices of the collective coordinates can steer the reaction along different pathways, thus offering the possibility of choosing the most probable mechanism.
Abstract: We studied the thermal intramolecular and radical rearrangement of azulene to naphthalene by employing a novel metadynamics method based on Car–Parrinello molecular dynamics. We demonstrate that relatively short simulations can provide us with several possible reaction mechanisms for the rearrangement. We show that different choices of the collective coordinates can steer the reaction along different pathways, thus offering the possibility of choosing the most probable mechanism. We consider herein three intramolecular mechanisms and two radical pathways. We found the norcaradiene pathway to be the preferable intramolecular mechanism, whereas the spiran mechanism is the favored radical route. We obtained high activation energies for all the intramolecular pathways (81.5–98.6 kcal mol−1), whereas the radical routes have activation energies of 24–39 kcal mol−1. The calculations have also resulted in elementary steps and intermediates not yet considered. A few attractive features of the metadynamics method in studying chemical reactions are pointed out.

Journal ArticleDOI
TL;DR: The first total synthesis of the ristocetin aglycon is described employing a modular and highly convergent strategy enlisting an unusually facile and diastereoselective aromatic nucleophilic substitution reaction that benefits from substrate preorganization.
Abstract: The first total synthesis of the ristocetin aglycon is described employing a modular and highly convergent strategy. An effective 12-step (12% overall) synthesis of the ABCD ring system 3 from its amino acid subunits sequentially features an intramolecular aromatic nucleophilic substitution reaction for formation of the diaryl ether and closure of the 16-membered CD ring system (65%), a respectively diastereoselective (3:1, 86%) Suzuki coupling for installation of the AB biaryl linkage on which the atropisomer stereochemistry can be further thermally adjusted, and an effective macrolactamization (51%) for closure of the 12-membered AB ring system. A similarly effective 13-step (14% overall) synthesis of the 14-membered EFG ring system 4 was implemented employing a room-temperature intermolecular SNAr reaction of an o-fluoronitroaromatic for formation of the FG diaryl ether (69%) and a key macrolactamization (92%) with formation of the amide linking residues 1 and 2. The two key fragments 3 and 4 were coup...

Journal ArticleDOI
TL;DR: Novel palladium migration/arylation methodology for the synthesis of complex fused polycycles has been developed, in which one or more sequential Pd-catalyzed intramolecular migration processes involving C-H activation are employed.
Abstract: Novel palladium migration/arylation methodology for the synthesis of complex fused polycycles has been developed, in which one or more sequential Pd-catalyzed intramolecular migration processes involving C-H activation are employed. The chemistry works best with electron-rich aromatics, which is in agreement with the idea that these palladium-catalyzed C-H activation reactions parallel electrophilic aromatic substitution.

Journal ArticleDOI
TL;DR: Total syntheses of alkaloid 251F, a natural product detected from the skin extracts of the dendrobatid frog species Minyobates bombetes, and its racemic 3-desmethyl derivative are reported, with a Diels-Alder reaction initiated both syntheses and established four consecutive stereogenic centers.
Abstract: Total syntheses of alkaloid 251F (1), a natural product detected from the skin extracts of the dendrobatid frog species Minyobates bombetes, and its racemic 3-desmethyl derivative (2) are reported. A Diels-Alder reaction initiated both syntheses and established four consecutive stereogenic centers. Important to the synthesis of 2 was a first-generation ozonolysis/olefination/aldol strategy to convert a [2.2.1] bicyclic acid to the [3.3.0]bicyclooctane diquinane 4b. Further elaboration to an appropriate keto azide allowed for a key intramolecular Schmidt reaction to deliver the tricyclic core of the target molecule. In a second-generation approach, a tandem ring-opening/ring-closing metathesis reaction effected an overall [2.2.1] --> [3.3.0] skeletal rearrangement to deliver diquinane 4a. In similar fashion, 4a was manipulated to an appropriate keto azide, and an intramolecular Schmidt reaction generated the core cyclic architecture of 251F.

Journal ArticleDOI
TL;DR: A "ring expansion-annulation strategy" for the synthesis of substituted azulenes is described based on the reaction of beta'-bromo-alpha-diazo ketones with rhodium carboxylates and the preparation of the azulenyl amino acid derivative 110.
Abstract: A “ring expansion-annulation strategy” for the synthesis of substituted azulenes is described based on the reaction of β‘-bromo-α-diazo ketones with rhodium carboxylates. The key transformation involves an intramolecular Buchner reaction followed by β-elimination of bromide, tautomerization, and in situ trapping of the resulting 1-hydroxyazulene as a carboxylate or triflate ester. Further synthetic elaboration of the azulenyl halide and sulfonate annulation products can be achieved by employing Heck, Negishi, Stille, and Suzuki coupling reactions. Reaction of the azulenyl triflate 84 with pinacolborane provides access to the azulenylboronate 91, which participates in Suzuki coupling reactions with alkenyl and aryl iodides. The application of these coupling reactions to the synthesis of biazulenes, terazulene 101, and related oligoazulenes is described, as well as the preparation of the azulenyl amino acid derivative 110.

Journal ArticleDOI
TL;DR: The first total synthesis of (+)-tricycloclavulone having a unique tricyclo[5,3,0,01,4]decane skeleton and six chiral centers was achieved in a highly stereoselective manner.
Abstract: The first total synthesis of (+)-tricycloclavulone having a unique tricyclo[5,3,0,01,4]decane skeleton and six chiral centers was achieved in a highly stereoselective manner. It includes a catalytic enantioselective [2+2]-cycloaddition reaction using novel chiral copper catalyst, extremely effecting an intramolecular ester transfer reaction, and asymmetric reduction of the carbonyl group on the α-chain using Noyori's chiral ruthenium catalyst.

Journal ArticleDOI
TL;DR: The well-known "first generation" Grubbs metathesis complex is capable of catalyzing the intramolecular [3 + 2] cycloaddition of alk-5-ynylidenecyclopropanes and it appears that the species responsible for the catalysis is a ruthenium complex generated in situ from the Grubber carbene in the presence of the substrate.
Abstract: The well-known "first generation" Grubbs metathesis complex is capable of catalyzing the intramolecular [3 + 2] cycloaddition of alk-5-ynylidenecyclopropanes. It appears that the species responsible for the catalysis is a ruthenium complex generated in situ from the Grubbs carbene in the presence of the substrate.

Journal ArticleDOI
TL;DR: These studies, along with the corresponding electrochemically initiated reactions, provide insight into this fundamentally new pattern of reactivity and support the feasibility of expanding this novel reaction type.
Abstract: The first examples of anion radical cycloaddition induced by homogeneous electron transfer from chemical agents are described. Specifically, upon exposure to chrysene anion radical, bis(enone) substrates are found to engage in stereoselective intramolecular [2 + 2] cycloaddition. These studies, along with the corresponding electrochemically initiated reactions, provide insight into this fundamentally new pattern of reactivity and support the feasibility of expanding this novel reaction type.

Journal ArticleDOI
TL;DR: The enantioselective synthesis of the eunicellin ophirin B has been completed with a ring-closing metathesis providing efficient access to the oxonene ring and a highly diastereoselectively intramolecular Diels-Alder reaction results in the formation of the hydrobenzofuran portion of the molecule.
Abstract: The enantioselective synthesis of the eunicellin ophirin B has been completed. A ring-closing metathesis provides efficient access to the oxonene ring, and a highly diastereoselective intramolecular Diels-Alder reaction results in the formation of the hydrobenzofuran portion of the molecule.

Journal ArticleDOI
TL;DR: This Rh-catalyzed enyne cyclization reaction represents a new process for the synthesis of stereodefined alpha-halomethylene-gamma-butyrolactones, lactams, tetrahydrofurans, pyrrolidines, and cyclopentanes.
Abstract: The rhodium(1)-species-catalyzed cycloisomerization reaction of a wide spectrum of 1,6-enynes with an unusual intramolecular halogen shift was investigated. This Rh-catalyzed enyne cyclization reaction represents a new process for the synthesis of stereodefined alpha-halomethylene-gamma-butyrolactones, lactams, tetrahydrofurans, pyrrolidines, and cyclopentanes. Coordinatively unsaturated rhodium species ([Rh(COD)Cl](2) + dppb + AgSbF6) only catalyzes the reaction with enyne substrates bearing a Z-form double bond, while neutral rhodium species (RhCl(PPh3)(3)) Could catalyze enyne substrates bearing a Z- or E-form double bond to form the desired products and has a wider substrate scopes. The mechanism of the reaction was studied by the employment of control experiments with different enyne isomers, and a pi-allyl rhodium intermediate was suggested to explain the formation of the cyclic products with an intramolecular halogen shift.

Journal ArticleDOI
TL;DR: Extension of this intramolecular reaction to substituted indoles, and other reactive heterocycles, provides a convenient and rapid access to a range of pharmacologically interesting tri- and tetracyclic scaffolds.
Abstract: A novel solid-phase intramolecular Pictet−Spengler reaction is presented. The approach utilizes masked aldehyde building blocks protected as their N-Boc-1,3-oxazinanes for the clean generation of solid-supported aldehydes. When exposed to simple acidic treatment, the aldehyde functionality is rapidly released and becomes susceptible to nucleophilic attack from an amide nitrogen of the peptide backbone, which results in the formation of a highly reactive cyclic N-acyliminium ion. Subsequently, a quantitative and highly stereoselective Pictet−Spengler reaction takes place by attack of the indole from a neighboring tryptophan, thus appending two new N-fused rings to the indole moiety. Extension of this intramolecular reaction to substituted indoles, and other reactive heterocycles, such as furane and thiophenes, provides a convenient and rapid access to a range of pharmacologically interesting tri- and tetracyclic scaffolds. Finally, the reaction products may conveniently be released from the solid support (...