Showing papers on "Annulation published in 2001"
191 citations
TL;DR: This annulation methodology is particularly effective for aryl- or alkenyl-substituted alkynes and when electron-rich imines are employed, this chemistry can be extended to alkyl- substituting alkynes.
Abstract: A wide variety of substituted isoquinoline, tetrahydroisoquinoline, 5,6-dihydrobenz[f]isoquinoline, pyrindine, and pyridine heterocycles have been prepared in good to excellent yields via annulation of internal acetylenes with the tert-butylimines of o-iodobenzaldehydes and 3-halo-2-alkenals in the presence of a palladium catalyst. The best results are obtained by employing 5 mol % of Pd(OAc)2, an excess of the alkyne, 1 equiv of Na2CO3 as a base, and 10 mol % of PPh3 in DMF as the solvent. This annulation methodology is particularly effective for aryl- or alkenyl-substituted alkynes. When electron-rich imines are employed, this chemistry can be extended to alkyl-substituted alkynes. Trimethylsilyl-substituted alkynes also undergo this annulation process to afford monosubstituted heterocyclic products absent the silyl group.
176 citations
146 citations
139 citations
TL;DR: The intermolecular [3 + 2] annulation of azomethine ylides with 2(2-nitrophenyl)acrylate dienophiles followed by reductive heterocyclization affords the spiro(indole-pyrrolidine) ring system to accomplish a concise and highly enantioselective synthesis of (-)-horsfiline 1.
Abstract: The intermolecular [3 + 2] annulation of azomethine ylides with 2(2-nitrophenyl)acrylate dienophiles followed by reductive heterocyclization affords the spiro(indole-pyrrolidine) ring system. Hence, this enable us to accomplish a concise and highly enantioselective synthesis of (-)-horsfiline 1, based on chiral auxiliary-directed pi-face discrimination in the 1,3-dipolar cycloaddition of (1S,2R)-2-phenyl-1-cyclohexyl ester 4f with N-methylazomethine ylide.
132 citations
TL;DR: The applicability of this methodology to the preparation of a key tetracyclic subunit of the kopsane alkaloids was demonstrated and significant regio- and diastereocontrol was observed.
Abstract: Indoles which bear an alkyl substituent in the 3-position undergo a [3 + 2] annulation reaction when treated with 1,1-cyclopropane diesters in the presence of Yb(OTf)3 resulting in 2,3-cyclopentanoindolines Typically, the reactions are performed at elevated temperatures or at ultrahigh pressures In cases where steric crowding is an issue, ultrahigh pressures are required In reactions involving substituted cyclopropanes, significant regio- and diastereocontrol was observed When the substituent was aromatic or olefinic, the reactions took place at ambient temperature and pressure The applicability of this methodology to the preparation of a key tetracyclic subunit of the kopsane alkaloids was demonstrated
120 citations
TL;DR: The PCP pincer complex, IrH2{C6H3-2,6-(CH2P-t-Bu2)2} catalyzes the transfer dehydrogenation of primary and secondary alcohols.
Abstract: The PCP pincer complex, IrH2{C6H3-2,6-(CH2P-t-Bu2)2} (1) catalyzes the transfer dehydrogenation of primary and secondary alcohols Dehydrogenation occurs across the CO bond rather than the CC bon
104 citations
TL;DR: The gold(III)-catalyzed sequential amination/annulation reaction of 2-propynyl-1,3-dicarbonyl compounds with primary amines produces 1,2,3,5-substituted pyrroles in moderate to high yields.
Abstract: The gold(III)-catalyzed sequential amination/annulation reaction of 2-propynyl-1,3-dicarbonyl compounds 1with primary amines 2produces 1,2,3,5-substituted pyrroles 4 in moderate to high yields.
99 citations
TL;DR: In this paper, a variety of substituted β- and γ-carbolines have been prepared in good to excellent yields by the annulation of internal acetylenes by the tert-butylimines of N-substituted 3-iodoindole-2-carboxaldehydes and 2-haloindoles-3 carboxaldehes, respectively, in the presence of a palladium catalyst.
96 citations
TL;DR: A wide variety of substituted isoindolo[2,1-alpha]indoles have been prepared via annulation of internal alkynes by imines derived from o-iodoanilines in the presence of a palladium catalyst, providing an extremely efficient route for the synthesis of these tetracyclic heterocycles from readily available starting materials.
Abstract: A wide variety of substituted isoindolo[2,1-a]indoles have been prepared via annulation of internal alkynes by imines derived from o-iodoanilines in the presence of a palladium catalyst. This methodology provides an extremely efficient route for the synthesis of these tetracyclic heterocycles from readily available starting materials. The mechanism of this interesting annulation process appears to involve (1) oxidative addition of the aryl iodide to Pd(0), (2) alkyne insertion, (3) addition of the resulting vinylic palladium intermediate to the C−N double bond of the imine, (4) either electrophilic palladation of the resulting σ-palladium intermediate onto the adjacent aromatic ring derived from the internal alkyne or oxidative addition of the neighboring aryl carbon−hydrogen bond, and (5) reduction of the tetracyclic product and Pd(0). A variety of internal acetylenes have been employed in this annulation process in which the aromatic ring of the alkyne contains either a phenyl or a heterocyclic ring.
92 citations
TL;DR: The synthesis and reactivity of a novel class of quinone boronic esters are described, prepared utilizing a highly regioselective Dötz annulation of Fischer carbene complexes with alkynylboronates, and the propensity of this technique to prepare highly functionalized aromatic compounds in an expeditious fashion is demonstrated.
Abstract: This paper describes the synthesis and reactivity of a novel class of quinone boronic esters. These compounds are prepared utilizing a highly regioselective Dotz annulation of Fischer carbene complexes with alkynylboronates. All substrates studied to date provided a single regioisomeric arylboronic ester product; the origin of this selectivity is discussed in the context of steric and electronic effects. Additionally, these compounds have been found to undergo Pd-catalyzed coupling reactions with a range of aryl and allyl halides and provides a strategy for the selective and predictable preparation of highly substituted quinones and hydroquinones. Finally, the propensity of this technique to prepare highly functionalized aromatic compounds in an expeditious fashion is demonstrated in the total synthesis of dimeric carbazole (+/-)-bis-N-dimethylbismurrayaquinone-A 33.
TL;DR: In this article, the synthesis of indolocarbazoles was achieved via photochemical and thermal annulation reactions of chromium Fischer carbene complexes, which allows for facile incorporation of hydrogen bonding functionality which complements the pharmacophore contained within bioactive indolocal carbazole natural products.
TL;DR: Experimental evidence supports a two-step mechanism in which enolization is followed by a thermal 6pi-electrocyclic reaction of an intermediate quinone methide that led to the total synthesis of the reputed structure of an Ageratum juvenile hormone.
TL;DR: A synthesis of tetracycle 2 corresponding to the C(11)-C(26) fragment of pectenotoxin II is described, which features two highly stereoselective [3 + 2]-annulation reactions of chiral allylsilanes, generated via allylboration of aldehydes with the chiral gamma-silylallylborane 4 or the gamma-methicone 19 for construction of the highly substituted C and E rings.
TL;DR: L-catalyzed cyclization of these substrates can be induced to give preferentially either exo- or endo-cyclized products in good yield simply by changing the reaction solvent.
TL;DR: In this paper, homochiral primary amines, amino alcohols and α-amino esters have been reacted with 2-propynyl-1,3-dicarbonyl compounds under gold catalysis leading to 1,2,5-trisubstituted 3-acylpyrrole derivatives in moderate to high yields and high enantiomeric excess.
Abstract: Homochiral primary amines, amino alcohols and α-amino esters have been reacted with 2-propynyl-1,3-dicarbonyl compounds under gold catalysis leading to 1,2,5-trisubstituted 3-acylpyrrole derivatives in moderate to high yields and high enantiomeric excess.
TL;DR: A new strategy for the synthesis of substituted azulenes is reported, based on the reaction of beta'-bromo-alpha-diazo ketones with rhodium carboxylates, with synthetic utility enhanced by the ability of the triflate derivatives to participate in Suzuki coupling reactions.
TL;DR: The enantiomeric aglycones of pseudopterosins K-L and A-F were synthesised from (−)- and (+)-isopulegol respectively.
Abstract: The enantiomeric aglycones of pseudopterosins K–L and A–F are synthesised from (−)- and (+)-isopulegol respectively. Key features are (a) the construction of the C3 stereogenic centre by a directed epoxidation–reduction sequence (K–L); (b) the creation of the C3 stereogenic centre by a Pfaltz asymmetric conjugate reduction (A–F); (c) benzannulation of a cyclic ketone starting with an α-oxoketene-S,S-acetal to give a tetrahydronaphthol ether; and (d) a diastereoselective intramolecular electrophilic aromatic substitution using an allylic sulfone as the electrophilic trigger to complete the hexahydro-1H-phenalene core. An X-ray structure of compound 50 was determined.
TL;DR: A general preparation of pyridines 4a-f from stabilized ketones 3a-c and aryl ketones3d-f is described and the mechanism of the reaction was investigated by NMR and proceeds through the formation of a dienaminone intermediate.
Abstract: A general preparation of pyridines 4a−f from stabilized ketones 3a−c and aryl ketones 3d−f is described. The annulation of stabilized esters 3g,h gives access to the corresponding 2-pyridones 4g,h. The annulation reactions proceed in fair to excellent yields (46−87%) with vinamidinium hexafluorophosphate salts 2a−d containing electron-withdrawing groups at the β-position. The mechanism of the reaction was investigated by NMR and proceeds through the formation of a dienaminone intermediate.
TL;DR: A radical [3+2] annulation reaction with an N-centered radical has been developed and the reaction of alkenes with N-allyl-N-chlorotosylamide yields the corresponding pyrrolidine derivatives in good yields in the presence of Et3B as a radical initiator.
TL;DR: This novel synthetic approach provides a highly efficient method for diversification of the benzofuran scaffold for combinatorial synthesis.
TL;DR: Total synthesis of the immunosuppresant pironetin has been achieved by a synthetic route in which the connections between starting materials and the desired structure are readily discerned.
TL;DR: An enantioselective total synthesis of (+)-blastmycinone was accomplished using this annulation of allylic silanes with N-chlorosulfonyl isocyanate as the key step.
TL;DR: Two alternative annulation pathways involving either the enolate arylation or the addition to the ketone carbonyl group can operate in the Pd-catalysed intramolecular coupling of 2-haloanilines and ketones.
TL;DR: In this paper, the authors synthesize diphenylphosphinophenyl pyridine ligands from (−)-β-pinene, (−)-3-carene, (+)-2-carenes, and (−)-α-pinenes via Krohnke annulation as the key step and shown to effect ≤88% ee in Heck addition.
TL;DR: 8-O-Methylpopolohuanone E (2) was synthesized in a highly convergent manner starting from the cis-fused decalin derivative accessible from the (−)-Wieland−Miescher ketone analogue.
TL;DR: The cedrene carbon skeleton was rapidly assembled from a simple monocyclic precursor by the strategic use of a high yielding intramolecular Khand cyclization reaction.
TL;DR: In this paper, a range of functionalized vinylic derivatives (azido, amino, and carbodiimide groups) were prepared for conversion into pyrroloazaindoles 19-22, imidazo[1,x]-, (x = 5, 6, 7, 8), [2,6]-, and naphthyridines 28-30, 35-38 by thermal reaction.
Abstract: Heterocyclization of functionalized vinylic derivatives of imidazo[1,2-a]pyridines was explored experimentally and theoretically using semiempirical AM1 and ab initio methods. A range of functionalized vinylic derivatives (azido, amino, and carbodiimide groups) were prepared for conversion into pyrroloazaindoles 19-22, imidazo[1,x]-, (x = 5, 6, 7, 8), [2,6]-, and [2,7]naphthyridines 28-30, 35-38 by thermal reaction. In the case of vinylic groups in the 5 position, peri annulation also was observed. The experimental and theoretical data are compared and discussed.
TL;DR: In this paper, the reaction of α-aroylketene dithioacetals with esters of o -aminobenzoic acid under different conditions afforded preferentially 2-methylthio-3-,aroyal-quinolones and 2-anilino-3-roylquinolines through, respectively, α-arnylketene N, S -acetal and α-arroyl ketene aminal intermediates.