Showing papers on "Claisen rearrangement published in 2021"
TL;DR: In this paper, a Bronsted acid-catalyzed intramolecular hydroalkoxylation/Claisen rearrangement was proposed, allowing practical and atom-economical synthesis of a range of valuable spiro lactams.
Abstract: Described herein is a novel Bronsted acid-catalyzed intramolecular hydroalkoxylation/Claisen rearrangement, allowing practical and atom-economical synthesis of a range of valuable spiro lactams from readily available ynamides in generally good to excellent yields with excellent diastereoselectivities and broad substrate scope. Importantly, an unexpected dearomatization of nonactivated arenes and heteroaromatic compounds is involved in this tandem sequence. Moreover, the asymmetric version of this tandem cyclization is also achieved via efficient kinetic resolution by chiral phosphoric acid catalysis. In addition, [3,3]-rearrangement is proved to be kinetically preferred over the related [1,3]-rearrangement by theoretical calculations.
35 citations
TL;DR: In this article, a discussion of the reaction scope, mechanistic insights, and synthetic applications of the tandem cyclization/Claisen rearrangement has been presented, with a focus on single-metal catalysis and bimetallic catalysis.
13 citations
TL;DR: An unprecedented aromatic aza-Claisen rearrangement of arylpropargylammonium salts, generated in situ from arynes and tertiary propargYlamines, delivering structurally diverse 2-propargylanilines in moderate to good yields with high regioselectivity is reported.
Abstract: The charge-accelerated aza-Claisen rearrangement of ammonium salts serves as a key step in the construction of complex nitrogen-containing molecules. However, much less attention has been paid to the aromatic aza-Claisen rearrangement than to the aliphatic one. Herein, we report an unprecedented aromatic aza-Claisen rearrangement of arylpropargylammonium salts, generated in situ from arynes and tertiary propargylamines, delivering structurally diverse 2-propargylanilines in moderate to good yields with high regioselectivity. This rearrangement proceeds in the absence of strong bases or transition metals, is compatible with moisture and air, tolerates a wide variety of functional groups, and is amenable to forming 11- to 13-membered heterocycles with a triple bond. The 2-propargylaniline products were treated with aluminum chloride in ethanol to afford multisubstituted indoles in moderate to excellent yields. Finally, a series of deuterium-labeling experiments was performed to elucidate the reaction mechanism.
10 citations
TL;DR: In this article, an auto-tandem catalytic double allylic rearrangement of N-alloc-N-allyl ynamides was developed, which proceeds through two separate and distinct catalytic cycles with both decarboxylative Pd-π-ally l and Pd(0)-promoted aza-Claisen rearrangements occurring.
9 citations
TL;DR: In this paper, a transition-metal-free intermolecular Claisen rearrangement process was developed to introduce allyl and allenyl groups into the α position of tertiary amides.
7 citations
TL;DR: In this article, the first enantioselective para-Claisen rearrangement has been achieved, using a chiral aluminum Lewis acid, illicinole is rearranged to give (-)-illicinone A (er 87:13), which can then be converted into more complex Illicium-derived prenylated phenylpropanoids.
7 citations
TL;DR: In this article, it was shown that the key allylic vinyl acetals can be efficiently generated through alkene isomerization of their readily available regioisomeric counterparts (derived from allylic alcohols and α,β-unsaturated aldehydes), thus enabling the first systematic study of the substrate scope of this rearrangement, and the discovery of exceptionally mild conditions for its mediation by Lewis and Bronsted acids.
Abstract: The [3,3]-sigmatropic rearrangement of allylic vinyl acetals, first investigated by Coates nearly four decades ago, is set apart from other variants of the Claisen rearrangement owing to the versatile monoprotected 1,5-dicarbonyl motif featured in the products. Unfortunately, the synthetically elusive nature of the substrates has thus far precluded the widespread application of this attractive transformation. Herein, we show that the key allylic vinyl acetals can be efficiently generated through alkene isomerization of their readily available regioisomeric counterparts (derived from allylic alcohols and α,β-unsaturated aldehydes), thus enabling the first systematic study of the substrate scope of this rearrangement, as well as the discovery of exceptionally mild conditions for its mediation by Lewis and Bronsted acids.
6 citations
TL;DR: In this article, an asymmetric aza-Claisen rearrangement between enantioenriched α-chiral allylamines and allenones was found to proceed in the absence of catalysts and additives at room temperature.
Abstract: An unprecedented asymmetric aza-Claisen rearrangement between enantioenriched α-chiral allylamines and allenones was found to proceed in the absence of catalysts and additives at room temperature. ...
6 citations
TL;DR: In this paper, an eight-membered nitrogen-containing heterocycles were straightforwardly produced by a nickel-catalyzed cycloetherification and subsequent Claisen rearrangement of secondary and tertiary alcohols.
6 citations
TL;DR: In this article, the authors focused on the applications of the Claisen condensation in the total synthesis of natural products up to the beginning of 2021 and reviewed the related literatures up to 2019.
6 citations
TL;DR: The first total synthesis of racemic cudraisoflavone J is reported using a Claisen rearrangement and a Suzuki coupling reaction as the key steps to elucidate the absolute configuration of naturally occurring cudrania tricuspidata.
Abstract: Cudraisoflavone J (1), isolated from Cudrania tricuspidata, is a potent neuroprotective compound with a chiral center. Herein, we report the first total synthesis of racemic cudraisoflavone J (1) using a Claisen rearrangement and a Suzuki coupling reaction as the key steps. Racemic secondary alcohol was kinetically resolved to give (+)- and (-)-cudraisoflavone J with up to 97 and 88% enantiomeric excess, respectively. The modified Mosher's method was used to elucidate the absolute configuration of naturally occurring cudraisoflavone J.
TL;DR: Propargyl aza-Claisen rearrangement of 4-propargylaminoisoxazoles as discussed by the authors has been successfully converted to the corresponding ortho-allenyl aniline 6 under the current reaction conditions.
Abstract: Propargyl aza-Claisen rearrangement of 4-propargylaminoisoxazoles 1 proceeded in the presence of cationic gold(i) catalysts to give 4-amino-5-allenylisoxazoles 2 in good to high yields. The silyl group at the terminal alkyne and a cationic gold(i) catalyst bearing a sterically bulky ligand are essential for the generation of isolable allene intermediates. The N-protection of the generated 4-amino-5-allenylisoxazoles 2 allowed the isolation of 5-allenylisoxazoles 4 that have never been synthesized. N-Propargyl aniline 5 was successfully converted to the corresponding ortho-allenyl aniline 6 under the current reaction conditions.
TL;DR: Aphamines A-C (1, 3), three pairs of acyclic diterpene dimer enantiomers with an unprecedent ploymerization pattern, were discovered from Aphanamixis polystachya by NMR-guided isolation and chiral resolution as discussed by the authors.
TL;DR: In this article, a computational investigation of two reaction cascades occurring following the Claisen rearrangements of aryl propargyl ethers to the alternate ortho positions in unsymmetrical reactants is presented.
Abstract: We report a computational investigation of two reaction cascades occurring following the Claisen rearrangements of aryl propargyl ethers to the alternate ortho positions in unsymmetrical reactants. Our computations explain how substituents influence reactivity and regioselectivity. Rearrangement to the substituted ortho carbon leads to a tricyclo[3.2.1.0]octane core, while rearrangement to an unsubstituted ortho carbon leads to a benzopyran. Density functional theory with ωB97X-D indicates that these reactions involve rate-determining Claisen rearrangements followed by subsequent reaction cascades of the Claisen rearrangement products depending on the presence or absence of a substituent at the ortho carbon.
TL;DR: In this paper, a thermal O-to-C [1,3]-rearrangement of α-hydroxy acid derived enol ethers was achieved under mild conditions.
TL;DR: In this paper, an enantioselective total synthesis of mollebenzylanols A and B was achieved in 13 and 11 steps, respectively, through an approach involving stereo/regio-selective epoxidation, Claisen rearrangement and stereocontrolled dihydroxylation.
TL;DR: In the presence of a n-butylammonmonium guest, calix[3]arene[1]chromane 6 forms two stereoisomeric complexes stabilized by +N-H···O and cation···π interactions.
TL;DR: The first total synthesis of isocorniculatolide B, corniculatolate B, and corniculate C, consisting of isomeric cornicule skeletons, have been accomplished in a divergent manner as mentioned in this paper.
TL;DR: In this article, Isothioureas tethered to tertiary allylic amines is converted to carbodiimides through a reaction with AgOTf/Et3N.
Abstract: Expansion of the scope of the 1,3-diaza-Claisen rearrangement beyond bridged-bicyclic tertiary allylic amines has been investigated through a tethering strategy. Isothioureas tethered to tertiary allylic amines are converted to carbodiimides through a reaction with AgOTf/Et3N. Intramolecular cyclization of the tertiary allylic amine to the carbodiimide equilibrates with a zwitterionic intermediate. Heating the carbodiimide/zwitterion affords a rearrangement product. Heating carbodiimide/zwitterion with a deuterated allyl group results in the scrambling of the deuterium label, which is consistent with an ionic mechanism involving heterolytic cleavage of the allylic C-N bond, followed by trapping of the allyl cation at either terminal carbon. The ionic mechanism is attributed to silver salt contamination since pushing deuterium-labeled carbodiimide/zwitterion through silica gel prior to heating results in clean deuterium transposition consistent with a sigmatropic mechanism, and adding back silver salts results in deuterium scrambling. Overall, the tethering strategy broadens the scope of the rearrangement to simpler allylic substrates. Density functional theory (DFT) calculations of the sigmatropic rearrangement are in agreement with reactivity trends observed with reactions run under silver-free conditions.
TL;DR: The synthesis of difluoropropargyl vinyl ethers from ketones and aldehydes are synthesised using diffluoroprostargyl bromide dicobalt complexes for the synthesis of trifluoro-pyran under acid-catalyzed conditions.
Abstract: With the increasing importance of fluorine to medicinal chemistry and other areas, methods to access various fluorinated compounds are needed. Herein, we report the synthesis of difluoropropargyl vinyl ethers from ketones and aldehydes using difluoropropargyl bromide dicobalt complexes. We applied difluoropropargyl vinyl ethers to the synthesis of difluorodienone or difluoroallene under thermal conditions and trifluoro-pyran under acid-catalyzed conditions.
TL;DR: In this article, aza-Bellus-Claisen rearrangement was used for the synthesis of a group of monoterpene natural products bearing vicinal dichloride subunits.
TL;DR: In this paper, a review of name reaction-based approaches for analyte detection is presented, which can be classified into 11 types, such as Tsuji-Trost allylic cleavage, Suzuki-Miyaura coupling, Claisen rearrangement, benzil-cyanide reaction, intramolecular crossed-benzoin reaction, Michael addition reaction, Gabriel mechanism, 2-aza-Cope rearrangements, (i) Baeyer-Villiger reaction, (j) Beckmannn rearrange, and (k) Lossen rearr
Abstract: The design and synthesis of suitable chemodosimeters for the detection of toxic analytes has become challenging for new researchers nowadays in the molecular recognition field. Among different chemical reactions, name reaction-based approaches will help researchers to gain knowledge about different types of name reactions for different analytes, the mechanism of sensing using these reactions, the names of scientists who pioneered these name reactions, and also to explore unknown name reactions for unexplored analytes. In this context, we have reported different sensing strategies, i.e., name reaction-based approaches involved in designing various chemodosimeters during the past decades. The name reaction-based approaches have been classified into 11 types, such as (a) Tsuji–Trost allylic cleavage, (b) Suzuki–Miyaura coupling, (c) Claisen rearrangement, (d) benzil-cyanide reaction, (e) intramolecular crossed-benzoin reaction, (f) Michael addition reaction, (g) Gabriel mechanism, (h) 2-aza-Cope rearrangement, (i) Baeyer–Villiger reaction, (j) Beckmannn rearrangement, and (k) Lossen rearrangement. The focus of the review is mainly on how name reactions are used in analyte detection chemodosimetrically.
TL;DR: In this paper, a novel and concise synthesis towards DP2 receptor antagonist Fevipiprant (NVS-QAW039) was developed by introducing the side chain early via reductive amination between the functionalized aldehyde and 2-amino-3-bromopyridine.
TL;DR: In this article, the authors reported an Au(I)-catalyzed hydroalkoxylation/Claisen rearrangement cascade reaction of aryl ynol ethers and ynamides with allylic alcohols.
Abstract: Polarized alkynes such as ynol ethers and ynamides have attracted much attention due to their inherent unique reactivity. Herein, we report Au(I)-catalyzed hydroalkoxylation/Claisen rearrangement cascade reactions of aryl ynol ethers and ynamides with allylic alcohols. At the first stage (hydroalkoxylation) of this cascade reaction, attack of allylic alcohols to aryl ynol ethers or ynamides occurs at the α-position of the polarized alkynes in a completely regioselective manner. Claisen rearrangement of the resulting adducts subsequently takes place to give γ,δ-unsaturated esters or amides, respectively. The [Au(IPr)NTf2] catalyst is most effective for this reaction, and the reaction proceeds under mild conditions (in the case of aryl ynol ether: in THF, 60 °C; in the case of ynamides: in toluene, 80 °C) in an atom-economical way.
TL;DR: In this article, an alternative route to perophoramidine core structure involving a N-chlorosuccinimde-mediated intramolecular cyclization reaction is reported, with an unexpected deep-seated rearrangement of the core structure occurring during an attempted iodoetherification reaction.
Abstract: The bioactive natural product perophoramidine has proved a challenging synthetic target. An alternative route to its indolo[2,3-b]quinolone core structure involving a N-chlorosuccinimde-mediated intramolecular cyclization reaction is reported. Attempts to progress towards the natural product are also discussed with an unexpected deep-seated rearrangement of the core structure occurring during an attempted iodoetherification reaction. X-ray crystallographic analysis provides important analytical confirmation of assigned structures.
TL;DR: In this article, the introduction of a nitrogen atom at either C-2' or C-3' positions of nucleosides derived from uridine, 4-N-benzoylcytidine and adenosine was investigated.
Abstract: Stereocontrolled introduction of a nitrogen atom at either C-2' or C-3' positions of nucleosides derived from uridine, 4-N-benzoylcytidine and adenosine was investigated. An efficient and rapid procedure was employed for creating new chiral centers at C-2' and C-3' positions using [3,3]-sigmatropic aza-Claisen rearrangement of allyl thiocyanates under conventional and microwave conditions. Structure of isothiocyanate products was confirmed by 1-D and 2-D NMR spectral analyses including selective 1H 1-D-NOE experiments.
TL;DR: A six-step synthesis of xanthohumol and its d3-derivative from easily accessible naringenin is reported.
Abstract: A six-step synthesis of xanthohumol (1a) and its d3-derivative (1b) from easily accessible naringenin is reported. The prenyl side chain was introduced by Mitsunobu reaction followed by the europium-catalyzed Claisen rearrangement and base-mediated opening of chromanone gave access to an α,β-conjugated ketone system. Compound 1b was used as an internal standard in stable isotope dilution assays of 1a in two Polish beers.