Showing papers on "Claisen rearrangement published in 1992"
176 citations
TL;DR: A solvent rate effect equation which uses four physical properties of the solvent for parameters has been applied with good success to solvolysis reactions, solvent E t values, Claisen Rearrangements, Diels-Alder reactions, endo-exo ratios in Dields-Ald reactions, azo-Cope rearrangements, and enol-ketone equilibria of the dimedone and pyridone variety as mentioned in this paper.
Abstract: A solvent rate effect equation which uses four physical properties of the solvent for parameters has been applied wiht good success to solvolysis reactions, solvent E t values, Claisen Rearrangements, Diels-Alder reactions, endo-exo ratios in Dields-Alder reactions, azo-Cope rearrangements, and enol-ketone equilibria of the dimedone and pyridone variety
92 citations
TL;DR: In this article, a self-consistent field solvation model was applied to the Claisen rearrangement of allyl vinyl ether, all possible methoxy-substituted derivatives, two alkylated derivatives, and one carboxymethylated derivative to understand the effects of aqueous solvation on the reaction rates.
Abstract: We report the results of applying a new self-consistent-field solvation model to the Claisen rearrangement of allyl vinyl ether, all possible methoxy-substituted derivatives, two alkylated derivatives, and one carboxymethylated derivative in order to understand the effects of aqueous solvation on the reaction rates. We have employed the AM 1-SM2 version of the model to calculate the changes in free energies of solvation in passing from the lowest-energy conformations of the starting materials to both chair and boat transition states. The hydrophobic effect is always accelerative but always small and not very structure sensitive
88 citations
TL;DR: The behavior of thioaldehydes, thioketones, thiono esters (O-alkyl thioates) and dithio esters, S-kyl dithiolates have been reviewed in this article.
Abstract: The behavior of thioaldehydes, thioketones, thiono esters (O-alkyl thioates) and dithio esters (S-alkyl dithioates) has been reviewed. Specific properties of thiocarbonyl compounds have been shown: Michael addition reaction of enethiolates, thiophilic addition of nucleophiles, easy thio-Claisen rearrangement, [4+2] cycloaddition with dienes and rich dipolarophile chemistry
86 citations
45 citations
TL;DR: In this article, the β-amino acid derivative was derived from (L)-aspartic acid, by the allylic chloride 12b followed by deprotection and lactonization leads to the nine-membered azalactone 18.
Abstract: N-Alkylation of the β-amino acid derivative 16, derived from (L)-aspartic acid, by the allylic chloride 12b followed by deprotection and lactonization leads to the nine-membered azalactone 18. Enolate Claisen rearrangement of this leads stereospecifically, via a boat-like transition state (cf. 6), to the pyrrolidine acid 19; subsequent one-carbon homologation, oxidation and deprotection affords (–)-(α)-kainic acid 1.
37 citations
TL;DR: In this article, the authors described a precise examination of the rearrangement of an aryl propargyl ether in the presence of CsF led to exclusive formation of 2-methylarylfuran in excellent yield.
Abstract: Claisen rearrangement of an aryl propargyl ether in the presence of CsF led to exclusive formation of 2-methylarylfuran in excellent yield. The result of a precise examination of the rearrangement is described. Satisfactory transformation of the 2-methylarylfuran to a salicylaldehyde derivative was achieved by stepwise oxidation. This combination of reactions serves as a useful method for regioselective introduction of a C1 unit at the ortho position of a phenol group.
36 citations
TL;DR: Aza-Claisen rearrangement of enolates of N-alkyl-N-(2E)-butenylpropanamides with chiral alkyl groups as discussed by the authors showed high relative asymmetric induction as well as excellent internal symmetric induction to give optically active NalkylPsyn-2,3-dimethylpent-4-enamides.
34 citations
32 citations
TL;DR: In this article, a commercial microwave oven accelerates the three-step ortho ester Claisen rearrangement of allyl and propynyl alcohols in dry DMF in open Erlenmeyer flasks.
Abstract: Microwave irradiation, using a commercial microwave oven accelerates (in 10–15 min) the three-step ortho ester Claisen rearrangement of allyl and propynyl alcohols in dry DMF in open Erlenmeyer flasks.
30 citations
TL;DR: The synthesis of rotationally restricted phenolic analogs of 5-hydroxyindole has been studied in this paper, where the synthesis of 8.9-dihydropyrano[3,2-e]indole (13a) and 7,8-diphysynylindole[2,3-f]indoles (13b) were obtained.
TL;DR: In this paper, 2-cyclohexenone rings that form part of a larger structural assembly are amenable to peracid oxidation with formation of an epoxy lactone.
Abstract: 2-Cyclohexenone rings that form part of a larger structural assembly are amenable to peracid oxidation with formation of an epoxy lactone. These intermediates are readily transformed under acidic, basic, or neutral conditions to ring-contracted aldehydo lactones, which are then subjected to condensation with a slight excess of Tebbe reagent. These conditions result in methylenation of carbonyl groups and set the stage for operation of a Claisen rearrangement. When the latter is catalyzed by Tribal, the sigmatropic process occurs at room temperature. With systems typified by 17 and 24, the isomerization is complete within 15 min. The presence of a proximate angular methyl group as in 9b, 29, and 37 exerts a retarding kinetic effect. In such examples, a period of 6 h is required to achieve completion. Swern oxidation completes the conversion to the 4-cyclooctenones, where the two carbons stemming from the Tebbe reagent are inserted between the original carbonyl and α-olefinic carbons. The overall process is...
TL;DR: In this paper, the synthesis of enantiomerically homogeneous N-methyl pipecolic esters from 1-amino-3-buten-2-ols is reported.
Abstract: The synthesis of racemic and enantiomerically homogeneous pipecolic esters from 1-amino-3-buten-2-ols is reported. The synthesis of enantiomerically homogeneous N-methylpipecolic esters requires four chemical steps from N-t-BOC-protected amino esters. The key step of the sequence is a conformationally restricted Claisen rearrangement. The method affords complete control of the absolute and relative stereochemistry of all three stereogenic centers in pipecolic ester 22 which is obtained in 33% overall yield from N-t-BOC-L-alanine ethyl ester 16a
TL;DR: The utility of the Claisen rearrangement using carefully separated, diastereoisomeric allylic alcohols in the preparation of (±)-Z-geissoschizol (4a, 3b, 5a, 6a and 6b) is discussed in this paper.
Abstract: The utility of the Claisen rearrangement using carefully separated, diastereoisomeric allylic alcohols (1a) and (1b) in the preparation of (±)-Z-geissoschizol (4a), (±)-3-epi-Z-geissoschizol (4b), (±)-corynantheidol (7a), (±)-dihydrocorynantheol (8a), (±)-3-epi-dihydrocorynantheol (8b) and the corresponding corynan-17-oic acid methyl esters (3a, 3b, 5a, 6a and 6b) is shown. Special attention is paid to the stereochemical outcome of catalytic (PtO 2 ) hydrogenation of the C(20) Z-ethylidene side chain
TL;DR: In this paper, Allenyl(aryl)iodinanes, generated from p-methoxy(diacetoxyiodo)arenes by the reaction with propyn-2-yl(trimethyl)silanes in the presence of BF3-Et2O in dichloromethane, undergo reductive ipso iodonio-Claisen rearrangement selectivity at -20 °C yielding ipso-substituted propynylarenes.
Abstract: Allenyl(aryl)iodinanes, generated from p-methoxy(diacetoxyiodo)arenes by the reaction with propyn-2-yl(trimethyl)silanes in the presence of BF3–Et2O in dichloromethane, undergo reductive ipso iodonio-Claisen rearrangement selectivity at –20 °C yielding ipso-substituted propynylarenes.
TL;DR: In this paper, a trifluoroacetic acid/water mixture under argon at room temperature is used to synthesize benzopyrans, which can be efficiently synthesized by reacting a phenol and an allylic alcohol in a trifeacetyl acid and water mixture.
TL;DR: In this article, the preparation of new glyco-organic substrates, along with their enhanced reactivity in water-promoted Claisen rearrangement, are described, and the chirality induced by the glucose moiety during the course of the reaction is dependent upon the α- or β-configuration of the anomeric centre.
Abstract: The preparation of new glyco-organic substrates, along with their enhanced reactivity in water-promoted Claisen rearrangement, are described. The chirality induced by the glucose moiety during the course of the reaction is dependent upon the α- or β-configuration of the anomeric centre. This allowed us to prepare enantiomerically pure (R) or (S) 1,3-diols 8, with D-glucose, as the unique source of chirality.
TL;DR: The Claisen rearrangement of the vinyl substituted ketene aminals 4a-c which were generated in situ by selenoxide elimination of the aminal precursors 3a,c in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene gave the monocyclic unsaturated medium ring lactams.
TL;DR: In this article, CsF-mediated Claisen rearrangement of an aryl propargyl ether to a 2-methylbenzolfuran and oxidative cleavage of the furan ring to a salicylaldehyde was used to synthesize chelerythrine, a benzo[c]phenanthridine alkaloid.
Abstract: By taking advantage of our novel synthetic methods involving CsF-mediated Claisen rearrangement of an aryl propargyl ether to a 2-methylbenzolfuran and oxidative cleavage of the furan ring to a salicylaldehyde, total synthesis of chelerythrine, a benzo[c]phenanthridine alkaloid, was accomplished via the common intermediate (5) prepared through the two routes shown in Chart 3.
TL;DR: In this paper, α-propargyloxyimines gave 2-amino-2-allenylketones by rearranging the tautomeric secondary enamine.
TL;DR: In this article, syn β-hydroxy γ-methyl dithioacetals were deprotonated with two equivalents of LDA and a subsequent S-alkylation of the resulting dianions yielded α-hydrox S-allyl ketene dithiacetals.
TL;DR: In this article, a base-catalyzed furan ring transfer reaction of the optically active (S)-tetrahydrobenzofuranyl propargyl ether followed by Claisen rearrangement was used to obtain a tricyclic furan with Sconfiguration.
TL;DR: In this paper, the C/D cis Grundmann ketone was converted by stereospecific Claisen and intramolecular Diels-Alder reactions of methyl 3-hydroxy-2-methylpropionate to a vitamin D synthon.
Abstract: Conversion by stereospecific Claisen and intramolecular Diels-Alder reactions of(+) methyl 3-hydroxy-2-methylpropionate to a vitamin D synthon, the C/D cis Grundmann ketone
TL;DR: The organoaluminum-promoted Claisen rearrangement of allylic vinyl ethers has been mechanistically studied by two sets of experiments and the observed Z and E selectivity is best accounted for by two possible chair-like structures with R substituents axial and equatorial, respectively as mentioned in this paper.
Abstract: The organoaluminum-promoted Claisen rearrangement of allylic vinyl ethers has been mechanistically studied by two sets of experiments and the observed Z and E selectivity is best accounted for by two possible chair-like structures with R substituents axial and equatorial, respectively.
TL;DR: In this paper, the thio-Claisen transposition of precursors bearing a stereogenic center adjacent to carbon 1 of the pericyclic nucleus has been investigated in the sulfur series.
TL;DR: In this paper, a number of chiral allylic alcohols have been prepared and submitted to a Mitsunobu reaction with dithioacetic acid, and the diastereoselectivity of this sigmoidropic shift was examined with respect to the nature of the two substituents at the stereogenic centre.