Showing papers on "Claisen rearrangement published in 2009"
TL;DR: Results suggest that face-selective olefin coordination is the enantioselectivity-determining step, which is almost exclusively controlled by the element of planar chirality in the asymmetric aza-Claisen rearrangements.
Abstract: Systematic studies have been performed to develop highly efficient catalysts for the asymmetric aza-Claisen rearrangement of trihaloacetimidates. Herein, we describe the stepwise development of these catalyst systems involving four different catalyst generations finally resulting in the development of a planar chiral pentaphenylferrocenyl oxazoline palladacycle. This complex is more reactive and has a broader substrate tolerance than all previously known catalyst systems for asymmetric aza-Claisen rearrangements. Our investigations also reveal that subtle changes can have a big impact on the activity. With the enhanced catalyst activity, the asymmetric aza-Claisen rearrangement has a very broad scope: the methodology not only allows the formation of highly enantioenriched primary allylic amines, but also secondary and tertiary amines; allylic amines with N-substituted quaternary stereocenters are conveniently accessible as well. The reaction conditions tolerate many important functional groups, thus providing stereoselective access to valuable functionalized building blocks, for example, for the synthesis of unnatural amino acids. Our results suggest that face-selective olefin coordination is the enantioselectivity-determining step, which is almost exclusively controlled by the element of planar chirality.
110 citations
TL;DR: The enantioselective synthesis of (+)-meloscine represents the first example of a natural product synthesis employing an enantiOSElective [2+2]-photocycloaddition as its key step, and illustrates nicely the synthetic potential of photochemical transformations for the construction of complex heterocyclic structures.
Abstract: The stereogenic centers at C3 and C12 of meloscine (3) can be established in the photochemical key step 1 → 2. 1,2-retro-Benzilic acid rearrangement to a five-membered ring, reductive amination, Claisen rearrangement, and ring-closing metathesis are further key steps in the transformation of cyclobutane 2 into the target molecule 3 (14 steps, 9 % overall yield). Enantioselective access to (+)-meloscine was possible when the [2+2]-photocycloaddition was conducted in the presence of a chiral template.
The unusual monoterpenoid indole alkaloid meloscine was synthesized starting from a protected aminoethylquinolone in 15 steps and an overall yield of 9 %, employing a [2+2]-photocycloaddition as the stereochemistry defining key step. After the initial plan of a Wagner–Meerwein type rearrangement of a [4.2.0]- into a [3.3.0]-bicyclic substructure could not be realized, the required ring enlargement of a cyclobutane was eventually achieved by a retro-benzilic acid rearrangement. Generation of the central pyrrolidine ring was possible by a three-step reductive amination domino sequence. The final ring was built up by a ring-closing metathesis after the last quaternary stereocenter had been constructed by a Johnson–Claisen rearrangement. The synthesis was concluded by a selenylation–elimination sequence to build up the exocyclic vinyl group of meloscine. Using our methodology for enantioselective [2+2]-photocycloaddition mediated by a chiral complexation agent, the experimentally very simple synthesis could be performed in an enantioselective fashion (7 % overall yield). The enantioselective synthesis of (+)-meloscine represents the first example of a natural product synthesis employing an enantioselective [2+2]-photocycloaddition as its key step, and illustrates nicely the synthetic potential of photochemical transformations for the construction of complex heterocyclic structures.
80 citations
57 citations
TL;DR: The formation of indoles was proven to be derived from an o-allenylaniline intermediate, which was generated by the Rh(I)-catalyzed amino-Claisen rearrangement of N-propargylanilines.
Abstract: Mild and facile preparations of 2-substituted or 2,3-disubstituted indole compounds were achieved by RhH(CO)(Ph(3)P)(3) (4-10 mol %)-catalyzed reaction of N-propargylanilines in hexafluoroisopropyl alcohol (HFIP). The formation of indoles was proven to be derived from an o-allenylaniline intermediate, which was generated by the Rh(I)-catalyzed amino-Claisen rearrangement of N-propargylanilines. The catalytic system is also available for the one-pot synthesis of indoles by reacting N-alkylaniline (1 equiv) with propargyl bromide (1.3 equiv) in the presence of K(2)CO(3) (3 equiv) in HFIP. The active catalyst was proven to be [Rh(CO)(Ph(3)P)(2)]OCH(CF(3))(2) generated in situ from RhH(CO)(Ph(3)P)(3) and HFIP. The structure of [Rh(CO)(Ph(3)P)(2)]OCH(CF(3))(2) was confirmed by single-crystal X-ray crystallographic analysis.
49 citations
TL;DR: Appropriately substituted nonracemic allyl alcohols, readily prepared from the corresponding enones by application of the CBS methodology, were converted to optically active cycloheptenone derivatives with almost complete transfer of chirality via an efficient "one-pot", cycloisomerization/Claisen rearrangement process.
47 citations
TL;DR: A successful asymmetric total synthesis of lycoposerramine-C involving such key steps as a cobalt-mediated Pauson-Khand reaction and vinyl Claisen rearrangement and its biomimetic transformation to phlegmariurine-A are described.
45 citations
TL;DR: In this paper, a facile aza-Claisen rearrangement was used to obtain 2-C-Methylene-N-glycosyl amides from 2-(hydroxymethyl) glycals.
39 citations
TL;DR: The total synthesis of the marine alkaloid halichlorine is described, based on an approach that involves constructing the fully substituted asymmetric center at an early stage.
Abstract: The total synthesis of the marine alkaloid halichlorine is described, based on an approach that involves constructing the fully substituted asymmetric center at an early stage. The five-membered ring is formed by 5-exo-trig radical cyclization and the unsaturated six-membered ring by a process that formally represents a sequential combination of conjugate addition and S(N)2' displacement-a method that is general for making bicyclic compounds with nitrogen at a ring fusion position. A formal synthesis of (+)-halichlorine is also reported, based on the development of a general method for preparing optically pure piperidines. The key step of this method, which was used to make one of our intermediates, is the Claisen rearrangement of a 4-vinyloxy-3,4-dihydro-2H-pyridine-1-carboxylic acid benzyl ester. Such O-vinyl compounds are easily generated in situ from the corresponding alcohols, which are themselves readily assembled from serine and terminal acetylenes.
39 citations
TL;DR: Inspired by this development, substituent and solvent rate effects are studied, and evidence that a chairlike transition state is highly favorable for the uncatalyzed Gosteli-Claisen rearrangement is provided.
Abstract: The results of kinetic studies on the uncatalyzed [3,3]-sigmatropic rearrangement of 2-alkoxycarbonyl-substituted allyl vinyl ethers are reported. Apparently first reported by Gosteli in 1972, this variation of a Claisen rearrangement enjoyed a shadowy existence for three decades until its potential for the development of a catalytic asymmetric Claisen rearrangement was discovered. Inspired by this development, we have studied substituent and solvent rate effects, and we provide evidence that a chairlike transition state is highly favorable for the uncatalyzed Gosteli-Claisen rearrangement.
37 citations
TL;DR: The total syntheses of cyclic nitrone-containing phlegmarine-type Lycopodium alkaloids, lycoposerramines-X and -Z, were accomplished starting from (R)-3-methylcyclohexanone via Pd-catalyzed Suzuki-Miyaura coupling, Johnson-Claisen rearrangement, stereoselective hydroboration-oxidation reaction, and Mitsunobu reaction, thereby establishing the structures including the absolute configuration.
Abstract: The total syntheses of cyclic nitrone-containing phlegmarine-type Lycopodium alkaloids, lycoposerramines-X and -Z, were accomplished starting from (R)-3-methylcyclohexanone via Pd-catalyzed Suzuki-Miyaura coupling, Johnson-Claisen rearrangement, stereoselective hydroboration-oxidation reaction, and Mitsunobu reaction, thereby establishing the structures including the absolute configuration.
32 citations
TL;DR: It is established that a cationic rhodium(I)-dppf complex catalyzes isomerizations of allyl propargyl ethers to allenic aldehydes in good yields from room temperature to 40 degrees C.
Abstract: We have established that a cationic rhodium(I)−dppf complex catalyzes isomerizations of allyl propargyl ethers to allenic aldehydes in good yields from room temperature to 40 °C. On the other hand,...
TL;DR: In this paper, a green way to synthesize allyl phenols has been developed using a fast Claisen rearrangement in a microreactor system without solvent and work-up.
TL;DR: The total syntheses of all stereoisomers of phenatic acid B and determination of their absolute configuration are described, based on an efficient combination of the Sharpless asymmetric dihydroxylation, the Johnson-Claisen rearrangement, and hydroboration-oxidation.
Abstract: The total syntheses of all stereoisomers of phenatic acid B and determination of their absolute configuration are described. The synthetic strategy is based on an efficient combination of the Sharpless asymmetric dihydroxylation, the Johnson−Claisen rearrangement, and hydroboration−oxidation. It involves 11−12 steps and overall yield of 5−8%.
TL;DR: Highly-selective, high-speed aromatic and aliphatic Claisen rearrangement was shown to give the corresponding product in an excellent yield induced by subcritical water microreaction in the absence of catalyst.
TL;DR: The uncatalyzed Gosteli-Claisen rearrangement of four double bond isomeric allyl vinyl ethers has been studied and the isolated assessment of the calculated ground-state or transition-state stabilities is not suitable to explain the experimentally observed structure-reactivity relationship.
Abstract: The uncatalyzed Gosteli−Claisen rearrangement of four double bond isomeric allyl vinyl ethers has been studied at the B3LYP/6-31G* and B3LYP/6-31G*+PCM levels of theory. The experimentally determined structure−reactivity relationship was successfully reproduced; the relative reactivity of the (E,E)-, (E,Z)-, (Z,E)-, and (Z,Z)-configured allyl vinyl ethers can be attributed to unfavorable interactions caused by pseudoaxial substituents within the chairlike transition-state structures. As expected, the isolated assessment of the calculated ground-state or transition-state stabilities is not suitable to explain the experimentally observed structure−reactivity relationship.
TL;DR: In this paper, the reactivity of oxazolones and their application in the synthesis of natural products is reviewed, focusing on the development and scope of Oxazolone-mediated ene-type reactions, 1,3-dipolar cycloadditions, and a novel Claisen-type rearrangement.
Abstract: This work reviews the reactivity of oxazolones and their application in the synthesis of natural products. In particular, the focus is on the development and scope of oxazolone-mediated ene-type reactions, 1,3-dipolar cycloadditions, and a novel Claisen-type rearrangement. The utility of these reactions towards natural product synthesis is described.
TL;DR: A bisamidinium catalyst has been designed for the Claisen rearrangement that can coordinate a singular oxygen atom of the substrate with the ability to function as a dual hydrogen donor.
TL;DR: In this article, the total synthesis of (-)-flustramine B was achieved via one-pot intramolecular Ullmann coupling and Claisen rearrangement.
Abstract: Total synthesis of (-)-flustramine B was achieved via one-pot intramolecular Ullmann coupling and Claisen rearrangement. A striking feature of this method of synthesis is that the sequential intramolecular Ullmann coupling and Claisen rearrangement reactions proceeds with concomitant deprotection of the methoxymethyl (MOM) group to afford spirocyclic oxindole with perfect asymmetric transmission in good overall yield.
TL;DR: In this article, a chiral allylic ester was used for the synthesis of the unusual epoxyketo amino acid Aoe found in chlamydocin, one representative of a group of peptide-based HDAc inhibitors.
TL;DR: A stereoselective synthesis of (+)-physoperuvine, a tropane alkaloid from Physalis peruviana Linne has been developed using a one-pot tandem aza-Claisen rearrangement and ring closing metathesis reaction to form the key amino-substituted cycloheptene ring.
Abstract: A stereoselective synthesis of (+)-physoperuvine, a tropane alkaloid from Physalis peruviana Linne has been developed using a one-pot tandem aza-Claisen rearrangement and ring closing metathesis reaction to form the key amino-substituted cycloheptene ring.
TL;DR: Biologically interesting 2,5-dihydrofuran-fused quinones were synthesized via the ruthenium-catalyzed [2 + 2 + 2] cycloaddition of an ether-tethered diiododiyne with alkynes, copper-Catalyzed Ullmann coupling of the resultant fused p-diiodobenzenes with methanol or allyl alcohol, and subsequent oxidation of phenol derivatives.
Abstract: Biologically interesting 2,5-dihydrofuran-fused quinones were synthesized via the ruthenium-catalyzed [2 + 2 + 2] cycloaddition of an ether-tethered diiododiyne with alkynes, copper-catalyzed Ullmann coupling of the resultant fused p-diiodobenzenes with methanol or allyl alcohol, and subsequent oxidation of phenol derivatives. The double Claisen rearrangement of the bis(allyl) ether product furnished a diallylhydroquinone derivative, which underwent iron-catalyzed oxidation, ring-closing metathesis, and dehydrogenation to deliver 1,3-dihydronaphtho[2,3-c]furan-4,9-dione.
TL;DR: In this paper, a highly enantioselective synthesis of 2,6-syn-disubstituted tetrahydropyrans from commercially available tri-O -acetyl-d -glucal, based on a thermal Claisen rearrangement, was proposed.
TL;DR: The synthesis of 2-methyltriclisine, an unnatural analog of the azafluoranthene alkaloid triclisine as mentioned in this paper, was achieved in 10 steps and 21'% overall yield from 2-bromo-3,4-dimethoxybenzaldehyde, through the intermediacy of 3,4dimethyloxyfluoren-9-one, and construction of the heterocyclic ring entailed the para-Claisen rearrangement of an allyl-4-fluorenyl ether, followed by isomerization of
TL;DR: An efficient synthetic protocol utilizing the sequential aromatic aza-Claisen rearrangement followed by the implementation of the intramolecular Heck reaction as a key step has been developed for the synthesis of various dibenzo-azocine derivatives of biological relevance.
TL;DR: The utility of 5-alkynyloxy, 5-propynylthio and 5-alkynylsulfinyl-pyrimidines as precursors of 7-substituted furo[3,2-d]- and thieno[3.2]-pyrimidine has been examined in this article.
TL;DR: Several alkynyl epoxides and one allyl alcohol were isomerized to cyclic allyl vinyl ethers (3,4-dihydro-2H-1,4oxazines) using PtCl2 as the catalyst as discussed by the authors.
TL;DR: A simple synthesis of the natural product honokiol 1 has been developed which proceeds in four steps and provides a 32% overall yield as mentioned in this paper, which is a Suzuki coupling of 4-allyl-2-bromoanisole 3 with 4-hydroxyphenyl boronic acid, followed by allylation.
TL;DR: The chiral vicinal diols prepared by asymmetric dihydroxylation in high enantioselectivities provide an excellent platform for separable diastereomers in the Johnson–Claisen rearrangement.
TL;DR: A one-pot, tandem process has been developed for the efficient synthesis of functionalised carbocyclic amides and an analogous cyclohexenyl trichloroacetamide was generated with high diastereoselectivity.
TL;DR: The Johnson-Claisen rearrangement of allyl alcohols with chiral vicinal diol functionality was employed to access chiral β,γ-disubstituted-γ-lactones in high enantio- and diastereoselectivity as discussed by the authors.
Abstract: The Johnson–Claisen rearrangement of allyl alcohols with chiral vicinal diol functionality was employed to access chiral β,γ-disubstituted-γ-lactones in high enantio- and diastereoselectivity. These were efficiently converted into nor-canadensolide, the advanced γ-(lactone–lactol) intermediate for xylobovide, canadensolide and sporothriolide and the lactone moiety of the santolinolides.