Sequential Claisen Research Articles

Synthesis of pyrimidine annulated furothiopyrans — An efficient sequential and tandem catalyzed Claisen rearrangement – intramolecular hydroaryloxylation

Regioselective synthesis of a hitherto unreported furothiopyran moiety fused at the C-5 and C-6 positions of a pyrimidine heterocycle was achieved by the application of sequential Claisen rearrangement in which a second aromatic Claisen rearrangement and intramolecular hydroaryloxylation were catalyzed by aluminum chloride. The second aromatic Claisen rearrangement step was also studied under thermal conditions to give mostly isomerized exocyclic compounds. The precursor endocyclic compounds were synthesized by thermal [3,3] sigmatropic rearrangement of the corresponding sulfide.Key words: aluminum chloride, sequential Claisen rearrangement, hydroaryloxylation, furothiopyran, pyrimidine.

Facile Construction of the Benzofuran and Chromene Ring Systems via PdII‐Catalyzed Oxidative Cyclization.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly Enantioselective Sequential Claisen—Ireland/Metathesis: Synthesis of Cycloalkenes Bearing Two Contiguous Highly Functionalized Asymmetric Centers.

Highly Enantioselective Sequential Claisen—Ireland/Metathesis: Synthesis of Cycloalkenes Bearing Two Contiguous Highly Functionalized Asymmetric Centers.

Facile Construction of the Benzofuran and Chromene Ring Systems via PdII-Catalyzed Oxidative Cyclization

[reaction: see text]. We herein report the development of one-pot procedures for the conversion of allyl aryl ethers to 2-methylbenzofurans (via sequential Claisen rearrangement and oxidative cyclization) and for the conversion of aryl homoallyl ethers to chromenes (via direct oxidative cyclization). It is likely that both reactions proceed via a common Pd-catalyzed pathway involving olefin activation, nucleophilic attack, and beta-hydride elimination.

Highly enantioselective sequential Claisen–Ireland/metathesis: synthesis of cycloalkenes bearing two contiguous highly functionalized asymmetric centres

A sequence of two reactions, consisting of a highly stereoselective silylated ketene acetal Claisen–Ireland rearrangement followed by a ring closing metathesis, gave a stereocontrolled access to various carbocycles.

A New Family of Macrocycles Produced by Sequential Claisen—Schmidt Condensations

AbstractFor Abstract see ChemInform Abstract in Full Text.

A new family of macrocycles produced by sequential Claisen-Schmidt condensations.

[reaction: see text] Members of a new family of macrocycles have been synthesized in one step, from simple building blocks, by sequential Claisen-Schmidt condensations.

Studies in Sigmatropic Rearrangement: Synthesis of a [6,6]Pyranothiopyran Ring System by Sequential Claisen Rearrangement and Pyridine Hydrotribromide Mediated Regioselective “6‐Endo” Cyclization.

[reaction: see text] 4-(4'-Aryloxybut-2'-ynylthio)[1]benzopyran-2-ones are refluxed in chlorobenzene to afford 4-aryloxymethylthiopyrano[3,2-c][1]benzopyran-5(2H)-ones which are subsequently subjected to heating in o-dichlorobenzene in the presence of N,N-diethylaniline and then treated with pyridine hydrotribromide to give [6,6]pyranothiopyrans in almost quantitative yield.

Efficient synthesis of novel carbocyclic nucleosides via sequential Claisen rearrangement and ring-closing metathesis

Very efficient synthetic route to novel 4′α- C-hydroxymethyl branched carbocyclic nucleosides was described. The stereocontrolled synthesis of target nucleosides was successfully achieved by Johnson orthoester–Claisen rearrangement, ring-closing metathesis (RCM) starting from a simple acyclic precursor 1,3-dihydoxy acetone 1 . Nucleosidic bases (adenine and cytosine) were coupled by Pd(0)-catalyzed allylic alkylation in a highly regiocontrolled manner.

Studies in sigmatropic rearrangement: synthesis of a [6,6]pyranothiopyran ring system by sequential claisen rearrangement and pyridine hydrotribromide mediated regioselective "6-Endo" cyclization.

[reaction: see text] 4-(4'-Aryloxybut-2'-ynylthio)[1]benzopyran-2-ones are refluxed in chlorobenzene to afford 4-aryloxymethylthiopyrano[3,2-c][1]benzopyran-5(2H)-ones which are subsequently subjected to heating in o-dichlorobenzene in the presence of N,N-diethylaniline and then treated with pyridine hydrotribromide to give [6,6]pyranothiopyrans in almost quantitative yield.

Progress toward the Synthesis of garsubellin A and related phloroglucins: the direct diastereoselective synthesis of the bicyclo[3.3.1]nonane core.

[reaction: see text] A highly diastereoselective single-step cyclization reaction provides access to the bicyclo[3.3.1]nonane core of the polyprenylated phloroglucin natural product garsubellin A. Further elaboration to a more functionalized analogue involves a sequential Claisen rearrangement/Grubbs olefin cross-metathesis strategy. Additionally, this strategy was extended to the preparation of the bis-quaternary carbon array found at the bridgehead positions of the phloroglucin natural products.

Studies in sulfur heterocycles. Part 16. Use of 7-hydroxy-1-benzothiophene in the synthesis of substituted benzothiophene derivatives and tricyclic compounds incorporating a fused thiophene ring

Heteroatom directed ortho-metallation on N,N-diethyl-7-carbamoyloxy-1-benzothiophene, readily available from 7-hydroxy-1-benzothiophene enabled regioselective substitution in the 6-position. Both 7- and 4-hydroxy-1-benzothiophene were used in the annelation of 5- or 6-membered oxygen heterocycles onto the 1-benzothiophene molecule through sequential Claisen rearrangement–ring closure reactions. The nature of the annelated ring depends upon the reaction conditions.

ChemInform Abstract: Cyclopentannulation by an Iterative Process of Sequential Claisen Rearrangement and Enyne Radical Closure: Routes to Triquinane and Propellane Systems and Use in the Synthesis of (.+‐.)‐Ceratopicanol.

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Cyclopentannulation by an Iterative Process of Sequential Claisen Rearrangement and Enyne Radical Closure: Routes to Triquinane and Propellane Systems and Use in the Synthesis of (±)-Ceratopicanol

Cycloalkenyl acetylenes 4, which are easily prepared from allylic alcohols by Claisen rearrangement and homologation (1 → 4), generally undergo radical cyclization (4 → 6) on treatment with stannyl radicals. The products (6) can themselves be converted into allylic alcohols, so that the annulation sequence can then be repeated. In certain cases enyne cyclization initiated by stannyl radicals does not work, but an alternative process (cf. Scheme 9) of epoxide opening with bis(cyclopentadienyl)titanium(III) chloride can then be used. Di- and triquinanes (Scheme 3) were made by the stannyl radical approach; the epoxide route was used to prepare a simple propellane (Scheme 4) and in a synthesis of (±)-ceratopicanol (Schemes 5 and 9).

A total synthesis of (−)-reiswigin a via sequential claisen rearrangement-intramolecular ester enolate alkylation

(−)-Reiswigin A ( 1), a novel anti-viral diterpene, has been synthesized in a highly stereoselective manner utilizing a sequential Claisen rearrangement — intramolecular ester enolate alkylation strategy.

An improved synthesis of trehalose 6-mono and 6,6′-dicorynomycolates and related esters

A simplified synthesis of 6-mono and 6,6′-di-corynomycolate esters of α,α-trehalose, and related compounds, was achieved by coupling the (hydroxyl-protected) acids to the partially trimethylsilylated sugar in the presence of dicyclohexylcarbodiimide and 4-dimethylaminopyridine. As acid reactants, (2- RS,3- RS)-3-hydroxy-2-tetradecyloctadecanoic acid ( dl-corynomycolic acid) and its 2 RS,3 SR diastereomer were prepared from methyl palmitate by sequential Claisen condensation, reduction, chromatographic separation, and saponification. Reaction with tert-butylchlorodimethylsilane (imidazole) gave the disubstituted ether-ethers, which were converted into the required 3- tert-butyldimethylsilyl ethers by partial hydrolysis. 6-Linked monocorynomycolate was obtained in excellent yield (78%) from the reaction of the RS, SR acid with the known heptakis- O-(trimethylsilyl)trehalose, and in good yield from equimolar portions of RS, RS acid and hexakis- O-(trimethylsilyl)trehalose. An excess (2.5-molar portions) of the RS, RS acid gave the 6,6′-diester (69%). The mono- and di-palmitate were similarly obtained from (Me 3Si) 6-trehalose. The mono ( RS, RS)-(Me 3Si) 6-trehalose coupling product was partially resolved on a silica gel column into its RR and SS diastereomers, the former corresponding to the naturally occurring trehalose monocorynomycolate. All coupling products were deprotected to free trehalose esters by treatment first with K 2CO 3 in methanol, then tetrabutylammonium fluoride-trifluoroacetic acid in oxolane.

Experiments Directed Towards the Synthesis of Anthracyclinones .XIV. An Intermediate for the Synthesis of Vineomycins

Anthrarufin (4) has been converted by a high-yielding route involving sequential reductive Claisen rearrangements into 1-acetoxy-5-methoxy-9,10-dioxo-6-(2'-oxopropy1)-9,10-dihydroanthracene-2-carbaldehyde (3), an intermediate which is suitable for the synthesis of vineomycins . The thermal Claisen rearrangements of some allyl ethers of 1,5-dihydroxyanthraquinone have been examined.

Studies on the sequential claisen rearrangement of methyl-3-arlyloxy- 2-(aryloymethyl)prop-2-enolates

Claisen rearrangement of methyl-3-aryloxy-2-(aryloxymethyl)prop-2-enoates ( 4) in refluxing N,N-diethylaniline gave 3-(2-hydroxyphenylmethylene) -3,4-dihydro-2H-1-benzopyran-2-ones ( 6) and 3-methoxycarbonyl-2H-1-benzopyrans( 7).

Synthesis of 3-substituted coumarins via sequential pericyclic transformations of δ-aryloxymethylacrylic acids and enophiles

A new procedure for the synthesis of 3-functionally substituted coumarins via sequential Claisen and ene reactions of δ-aryloxymethylacrylic acids and anophiles has been developed.

A Claisen rearrangement route to the vineomycins

Anthrarufin is converted by a high yield route involving sequential Claisen rearrangements to an intermediate (3) suitable for the synthesis of vineomycins