Showing papers on "Annulation published in 2000"
TL;DR: The breakthrough is presented using chiral phosphoramidite ligands for copper-catalyzed dialkylzinc additions for enantioselective carbon-carbon bond formation by 1,4-addition of organometallic reagents to enones.
Abstract: The development of an efficient catalytic system for enantioselective carbon−carbon bond formation by 1,4-addition of organometallic reagents (organolithium, Grignard, and organozinc reagents) to enones is a major challenge in organic synthesis. This Account presents the breakthrough realized in this field using chiral phosphoramidite ligands for copper-catalyzed dialkylzinc additions. Applications in catalytic routes to cycloalkanones as well as tandem and annulation procedures with excellent enantioselectivities are discussed.
595 citations
TL;DR: In this paper, a single-step enantioselective synthesis of the Wieland-Miescher ketone (5 ) is presented, and it is shown that l -proline as well as a number of other chiral amines can act as catalysts of both steps of the Robinson annulation reaction.
260 citations
175 citations
TL;DR: Regiospecific carbonylative annulation of o-iodophenol acetates and acetylenes mediated by palladium-thiourea-dppp complex in the presence of base at 40 degrees C under a balloon pressure of CO generates diversified flavones in high yields.
171 citations
149 citations
TL;DR: A variety of substituted coumarins have been prepared in good yields by the palladium-catalyzed coupling of o-iodophenols with internal alkynes and 1 atm of carbon monoxide.
119 citations
TL;DR: A highly effective cocatalysis system (PdI2-thiourea and CBr4) was developed for carbonylative cyclization of both electron-rich and electron-deficient o-hydroxylarylacetylenes to the corresponding methyl benzo[b]furan-3-carboxylates.
114 citations
100 citations
TL;DR: A number of synthetic strategies to the Cox-2 specific inhibitor 1 have been described, leading to the identification of a novel pyridine construction using annulation of ketone 2 using a vinamidinium species 29 and ammonia in 97% assay yield.
Abstract: A number of synthetic strategies to the Cox-2 specific inhibitor 1 have been described. These studies have led to the identification of a novel pyridine construction using annulation of ketone 2 using a vinamidinium species 29 and ammonia in 97% assay yield. Three approaches to the synthesis of ketone 2 are described that allow for its preparation in large quantities in >65% overall yield from methyl 6-methylnicotinate.
100 citations
TL;DR: A new strategy for enantiospecific construction of the Securinega alkaloids has been developed and applied in total syntheses of (+)-14,15-dihydronorsecurinine (8), (-)-norsecur inine (6), and phyllanthine.
Abstract: A new strategy for enantiospecific construction of the Securinega alkaloids has been developed and applied in total syntheses of (+)-14,15-dihydronorsecurinine (8), (−)-norsecurinine (6), and phyllanthine (2). The B-ring and C7 absolute stereochemistry of these biologically active alkaloids originated from trans-4-hydroxy-l-proline (10), which was converted to ketonitrile 13 via a high-yielding eight-step sequence. Treatment of this ketonitrile with SmI2 afforded the 6-azabicyclo[3.2.1]octane B/C-ring system 14, which is a key advanced intermediate for all three synthetic targets. Annulation of the A-ring of (−)-norsecurinine (6) with the required C2 configuration via an N-acyliminium ion alkylation was accomplished using radical-based amide oxidation methodology developed in these laboratories as a key step, providing tricycle 33. Annulation of the D-ring onto α-hydroxyketone 33 with the Bestmann ylide 45 at 12 kbar gave (+)-14,15-dihydronorsecurinine (8). In the securinine series, the D-ring was incorpo...
87 citations
TL;DR: In this article, an all-carbon dipole derived by the interaction of triphenylphosphine with allenic ester is able to locate the polarized 2π-component in 3-formylchromones through a regioselective [2 + 3] addition to the C2−C3 π-bond, which is followed by deformylation leading to novel 3a,9a-dihydro-1-ethoxycarbonyl-1 -cyclopenteno[5,4-b]benzopyran-4
TL;DR: Application of this methodology in syntheses of the antibiotics WS-5995A, WS- 5995C, and functional analogues was demonstrated, and antitumoral activity of this class was determined.
Abstract: Intramolecular palladium-mediated arylation approaches to benzo[b]fluorenes have been investigated. The methodology has been applied in a short synthesis of tri-O-methylkinafluorenone, providing an effective alternative to Friedel−Crafts-based approaches. During the course of this work, an acid-promoted quinolactonization of naphthoquinones was also developed, providing direct access to either ortho or para isomers as desired. Application of this methodology in syntheses of the antibiotics WS-5995A, WS-5995C, and functional analogues was demonstrated, and antitumoral activity of this class was determined.
TL;DR: The specific formation of (Z)-isomers from Horner–Wadsworth–Emmons reaction of phosphonylglycinates and 2-iodobenzaldehydes was crucial to the success of the process and the product N-substituted indole-2-carboxylates were isolated in high yield.
TL;DR: The reaction was applied to the preparation of the COX-2 specific inhibitor 5-chloro-3-(4-methylsulfonyl)phenyl-2-(2-methyl-5-pyridinyl)pyridine (1), as well as a series of analogues.
TL;DR: Benzene-1,2-diol reacts with various propargylic carbonates in the presence of a palladium catalyst and a chiral atropoisomeric diphosphine to give 2-alkylidene-3,alkyl,1,4-benzodioxanes in good yields and 56-97% enantiomeric excess.
TL;DR: In this article, the nickel-catalyzed annulations of electron-deficient allenes proceed efficiently in a highly regioselective manner under very mild conditions to give the head-to-head cyclodimerization products, bismethylenecyclobutanes, as single isomers in good to fair yields.
Abstract: The nickel-catalyzed [2 + 2] annulations of electron-deficient allenes proceed efficiently in a highly regioselective manner under very mild conditions to give the head-to-head cyclodimerization products, bismethylenecyclobutanes, as single isomers in good to fair yields. We also carried out the stoichiometric reaction of these allenes in the presence of Ni(0) complexes and elucidated the mechanism of this highly selective reaction.
TL;DR: The reactions of the radicals derived from indoles 4 are described leading to a short synthesis of fused [1,2-a]indoles via radical addition to the benzene ring followed by rearomatisation whilst one example undergoes an unusual radical translocation/addition reaction.
TL;DR: An efficient solid-phase approach has been developed to prepare nitrogen heterocycles with a 1,2,3,4-tetrahydro-2-pyridone core via aza-annulation of enamines via acolysis of primary amines with propynoic acid derivatives or ketones.
Abstract: An efficient solid-phase approach has been developed to prepare nitrogen heterocycles with a 1,2,3,4-tetrahydro-2-pyridone core via aza-annulation of enamines Immobilized enamines were prepared from the reaction of primary amines with propynoic acid derivatives or ketones Aza-annulation reactions were carried out by reacting resin-bound enamines with symmetrical alpha,beta-unsaturated acid anhydrides or alpha,beta-unsaturated acids in the presence of DPPA and TEA The annulation products were isolated in good to high crude yields Influence of sterically hindered amines as well as alpha- and beta-substituted acrylic acid derivatives on the annulation reaction was also investigated
TL;DR: In double stereodifferentiating reactions with in situ generated imines, good levels of selectivity were achieved in the formation of secondary amines bearing syn–anti and syn–syn stereochemical triads.
TL;DR: In this paper, β-Diketones, β-ketoesters and β -ketonitriles in the presence of propargyl bromide, DBU and a catalytic amount of CuI in toluene give 2,3,5-trisubstituted furans through sequential alkylation/cyclisation/isomerisation reactions.
TL;DR: In this article, aldehydes with 2-substituted 2-alkenals are formed 2,4-disubstitized 1-naphthols and/or 1,3-dissubstitized naphthalenes accompanied by decarbonylation.
TL;DR: In this paper, a new formal stereoselective synthesis of (+)-Huperzine A (1) was achieved using as a key step a palladium mediated annulation between 2-methylene-1,3-propanediol diacetate and (1R,2S)-2-phenylcyclohexanol derived β-ketoester 2c.
TL;DR: The tricyclic core of cyathins has been synthesized using a Brook rearrangement-mediated [3 + 4] annulation that was previously developed.
TL;DR: In this article, nonconjugated aromatic hexa-and heptaynes underwent domino thermal radical cycloaromatization at 25°C to yield indenol ring-fused fluoranthene skeletons with helicity.
TL;DR: Palladium-catalysed regio- and stereoselective annulation of allenyl stannanes by β-iodo vinylic acids gives the corresponding α-pyrones in high yields.
TL;DR: The 4 + 1 radical annulation reaction of aryl isonitrile with iodoalkynes or iodonitriles affording cyclopenta-fused pyridines and pyrazines is described in this paper.
Abstract: The 4 + 1 radical annulation reaction of vinyl isonitriles with iodoalkynes or iodonitriles affording cyclopenta-fused pyridines and pyrazines respectively and the first example of an intramolecular radical addition to an aryl isonitrile are described.
TL;DR: A protocol has been developed in which annulation reactions of various dihalides with keto esters can be carried out to provide entry to eight- and nine-membered carbocycles.
Abstract: A protocol has been developed in which annulation reactions of various dihalides with keto esters can be carried out to provide entry to eight- and nine-membered carbocycles. In this process wherein one alkenyl- or aryl bromide and a tethered alkyl chloride comprise the organic dihalide, a selective metal−halogen exchange reaction between the sp2-hybridized bromide and an organolithium initiates the process. Transmetalation to an organoytterbium reagent generates a species that undergoes selective carbonyl addition to the ketone of the keto ester, creating a lactone intermediate. Subjection of the resulting chloroalkyl lactone to intramolecular reductive coupling with samarium(II) iodide completes the desired annulation.
TL;DR: The benzhydryldimethylsilyl group has been used for annulation reactions of carbocycles and heterocycles with high stereoselectivities as discussed by the authors, and it has been shown to provide a variety of highly substituted five-membered carbocycocycicles and heterocyclic compounds.