Search

Diaddition of alkenyllithium to 1,2-diones induce dianionic oxy-Cope rearrangements. As 1,2-diones some 1,2-diarylethane-1,2-diones were treated with (4,5-dihydrofuran-2-yl)lithium. The reaction, which took place at -78 °C, stereoselctively afforded meso-3,3'-coupled bis(tetrahydrofurans), which, in contrast to their 2,2' counterparts, have so far hardly been investigated. Two of the reaction products were characterized by crystal structure analyses. Subsequent intramolecular aldol addition gave a highly substituted octahydro-2H-cyclopenta[1,2-b:4,3-b']difuran, whose constitution and relative configuration were determined by NMR including NOE measurements.

An effective method for the installation of isoprenyl moiety at the C1 position of xanthone has been developed. Addition of isoprenyl Grignard reagent to 1-fluoroxanthone derivatives proceeded γ-selectively, and the obtained tertiary alcohols underwent aromatic oxy-Cope rearrangement and subsequent elimination of fluoride anion under mild conditions to give 1-isoprenylxanthones in high yields.

Bis(iodozincio)methane, prepared from diiodomethane and zinc metal in the presence of a lead catalyst, is capable of performing several unique molecular transformations. It can operate not only as a dianion, but also as a bidentate Lewis acid. In this ­account, the methylenation of carbonyl compounds, nucleophilic cyclopropanation reactions, 1,4-addition reactions of bis(iodozincio)methane, and reduction reactions of π-allylpalladium are discussed, along with the associated density functional theory calculations. 1 Introduction 2 Methylenation of Carbonyl Compounds 3 Nucleophilic Cyclopropanation 3.1 Cyclopropanation of 1,2-Diketones 3.2 Asymmetric Construction of Quaternary Carbon Atoms by Stereospecific Cyclopropanation 4 1,4-Addition Reactions of Bis(iodozincio)methane 4.1 Three-Atom Ring-Contraction Reaction 4.2 Enolate–Homoenolate Intermediates and Their Reactions 5 Reduction of π-Allylpalladium Derivatives 6 Conclusions and Outlook

An effective method for the installation of isoprenyl moiety at the C1 position of xanthone has been developed. Addition of isoprenyl Grignard reagent to 1-fluoroxanthone derivatives proceeded γ-selectively, and the obtained tertiary alcohols underwent aromatic oxy-Cope rearrangement and subsequent elimination of fluoride anion under mild conditions to give 1-isoprenylxanthones in high yields.

(19R)-and (19S)-tert-Butyldimethylsilyl (TBS) ethers of 19-hydroxy-19-vinyl-16α,17α-cyclohexanopregn-5-en-20-ones were synthesized. These compounds containing the 1,5-oxydienoic motif were subjectedto the anionic oxy-Cope rearrangement to obtain 3β-TBS ether of 6β-(3-oxopropyl)-16α,17α-cyclohexano-19-norpregn-5(10)-en-20-one. The structures of the compounds synthesized were confirmed by the analysis of their 1H and 13C NMR spectra.

Polycyclic compounds have been prepared by aromatic dianionic oxy-Cope rearrangements involving the π bonds of two phenyl rings in a [3,3] sigmatropic rearrangement.

The sequential ester dienolate [2,3]-Wittig/oxy-Cope rearrangement/carbonyl ene reaction has been investigated. Acyclic α,β-unsaturated α-allyloxy-substituted esters 1a−j were transformed into cyclopentane- or cyclohexanecarboxylates 6a−f and 7a−7d. This study presents a domino ester dienolate [2,3]-Wittig/oxy-Cope rearrangement or a domino oxy-Cope rearrangement/carbonyl ene reaction, depending on the substrate structure. The thermal intramolecular type-I carbonyl ene reaction as the terminating ring-closing reaction proceeds with high simple diastereoselectivity, but low induced diastereoselectivity. The corresponding type-II ene reaction afforded the cyclohexanecarboxylates 7a−d in high yield with complete simple and induced diastereoselectivity. Unfortunately, an attempted auxiliary-controlled enantioselective sequence was inefficient.

Racemic β-hydroxycyclohexanones with up to three chiral centres have been synthesized in a stereocontrolled way using the novel anionic oxy-Cope (AOC) rearrangement of acyclic enol ethers. The first examples of compounds containing an aldehyde and an enol ether in a 1,5 relationship are reported. Stereocontrol in the cyclisation of these compounds by a 6-(enolendo)-exo-trig intramolecular aldol reaction has been studied: there is high stereoselectivity for an axial hydroxy group in the product β-hydroxycyclohexanones. AM1 calculations show that there is a stabilising electrostatic attraction between the oxygen atom of the axial C-3 hydroxy group and the electron-poor carbon at C-1 in the intermediate oxonium ions. ≥87% of AOC rearrangement occurs via a chair-like transition state giving rise to the 5,6-anti stereochemistry of the β-hydroxycyclohexanones. Trapping the enolate product of AOC rearrangement with oxygen gives fragmentation via a 1,2-dioxetane.

Dianionic oxy Cope rearrangements have been shown to take place at low temperature upon syn double addition of alkenyllithium derivatives to cyclobutanedione compounds such as benzocyclobutenedione chromium complex 1 or squaric acid esters. In order to obtain some insight into the more general applicability of this type of reaction sequence beyond these special cases, a number of 1,2-diketones were treated with vinyllithium. The diketones tested include benzil derivatives, aliphatic acyclic 1,2-diketones, ortho-quinones, and cyclic aliphatic 1,2-diketones. With benzil and heterobenzil derivatives, the desired double addition/dianionic oxy Cope rearrangement was found to take place at low temperature, leading to 1,6-diketones and their intramolecular aldol adducts in up to 80% overall yield. With acyclic aliphatic 1,2-diketones as substrates, this reaction sequence was also found, albeit with somewhat lower yields and requiring higher temperatures than in the benzil cases. A brief investigation of the intramolecular aldol adduct/1,6-hexanedione equilibrium indicated that the preferential formation of intramolecular aldol adducts at lower temperatures and at shorter reaction times appears to be the result of kinetic reaction control, whereas the preference for 1,6-diketones at higher temperatures is caused by thermodynamic reaction control. ortho-Quinones reacted with vinyllithium only by addition; no dianionic oxy Cope rearrangement was observed. This was also the case for most aliphatic cyclic diketones; however, in the case of 1,2-indanedione, rearrangement products were obtained in moderate yield at elevated reaction temperatures.

[(6-Methyl-1-oxa-4-thiaspiro[4.5]dec-6-en-7-yl)(allyl)methanols were subjected to anion-accelerated oxy-Cope rearrangement in solvents such as THF, benzene and DME to assess the π-facial selectivity caused by the acetal function. The diastereomeric pairs 17a and 17b (R = Ph) furnished the same two diastereomeric products 18a and 18b, differing only in the relative preponderance. The reaction of 17a turned from mostly syn to oxygen (18a∶18b = 1∶4) in THF to moderately syn to sulfur (18a∶18b = 2.2∶1) in DME. The reaction was completely nonselective in benzene. The effect of solvent on the reaction of 17b was even more interesting. The reaction turned from completely nonselective (18a∶18b = 1∶1) in THF to highly syn to sulfur (18a∶18b = 5.4∶1) in DME. The selectivity in benzene was somewhere in between (18a∶18b = 2.7∶1). Likewise, the reaction of 17b (R = H) turned from moderately syn to oxygen in THF (18a∶18b = 1∶2) to nearly nonselective in DME (18a∶18b = 1∶1.1). The rotation around the bond between the methanol carbon and the adjacent ring-carbon is restricted to allow rearrangement only syn to sulfur in 17a and syn to oxygen in 17b. The considerable erosion in the observed diastereoselectivity is due to a radical and/or ionic retroaldol–recombination process. The radical pathway, however, is more prevalent than the ionic alternative. The recombination favors somewhat the addition of the allyl radical to the cogenerated 7-benzoyl-6-methyl-1-oxa-4-thiaspiro[4.5]dec-6-ene on the face syn to the sulfur. As a result of such dissociation and recombination, the oxy-Cope rearrangement does not appear suitable as a probe for the study of diastereofacial selectivity.

The aromatic oxy-Cope rearrangement including a benzene ring took place when 1-methoxy-2-aryl-bicyclo[2.2.2]oct-5-en-2- exo -ols and 2-(2-methoxyphenyl)-bicyclo[2.2.2]oct-5-en- exo -2-ols were treated with KH in THF.

A short synthesis of (±)-palominol (1) and (±)-dolabellatrienone (2) starting from farnesol is reported. Noteworthy steps include an intramolecular pinacol coupling to form a 15-membered carbocyclic diol and subsequent dianion-accelerated oxy-Cope rearrangement to form the 11,5-trans-fused ring system of the dolabellanes.

This article has no abstract. Keywords: 2-Substituted benzofuranes; homotropilidene–palladium dichloride complexes; isomerization of allyl phenyl ethers and allyl phenols; π-allylpalladium chloride complexes; indenones; oligomerization; chlorination of steroids; chlorohydrins from epoxides; cope rearrangement; S N claisen rearrangement; steroidal π-allyl palladium complexes; chloroallylation; cyclization of alkynoic acids; oxy-cope rearrangement; Claisen rearrangement of allyl imidates; cleavage of propargyl vinyl ethers; allylation of aldehydes with allyl alcohols; cyclization of allyl propynoates; ArSo2Cl Arl; arenesulfonyl isocyanates; imidazolidin-2-thiones; enediynes; insertion of C = O into silacyclobutanes; α-vinyl-β-lactams; 2-methylene-1,4-alkanediols; hetero diels–alder reactions; Claisen rearrangement; Heck reaction; [3 + 2]cycloaddition; 1,2-addition to norbornenes; 2-arylpropionic esters; Claisen rearrangement; coupling reactions; dehalogenation; 3-allylfurans; coupling reactions; arenecarboxylic acids and derivatives; protecting group maneuvers; coupling reactions; 1,4-additions; styrenes; cyclization; reductive amination; coupling reactions; isomerization; π-allylpalladium chloride complexes; indenones; oligomerization; chlorination of steroids; chlorohydrins from epoxides; cope rearrangement; S N Claisen rearrangement; steroidal π-allyl palladium complexes; directed site-activation; addition; coupling reactions; Wacker reaction; 2-Benzothiazolylmethyl 2-oxoalkyl sulfones; hydroaminomethylation to alkenes; BINAMINE derivatives; BINOL-derived phosphites; cyclobutanol cleavage

A general method of synthesising functionalized title compounds via oxy-Cope rearrangement using sodium ethoxide is reported.

Linearly fused tricyclic [5.6.5] and [6.6.6] compounds 4, 6, 10 and 12 were prepared from ethynyl and allenyl derivatives of self condensed cycloalkanones 3, 5, 9 and 11 by thermal oxy-Cope rearrangement is described.

Condensation of α,β-unsaturated carbonyl compounds with y-trimethylsilylmethylallylzircocene followed by anionic oxy-Cope rearrangement provided a novel method for the synthesis of functionalized allylsilanes compounds possessing a carbonyl group in the same molecule, which are versatile intermediates for intramolecular allylsilylation, giving cyclopentanols on treatment with n-Bu 4 NF.

The title reaction is studied as both classical one-pot reaction and in a microflow system.

The base-catalyzed oxy-Cope rearrangement of systems incorporating an allenic π system was studied. The rearrangement incidentally leads to functionalized bicyclo[4.3.0]nonane 15, bicyclo[4.4.0]decanes 6 and 10, and 3,5-cycloundecadien-1-one 20. The effect of ring size and nature of the base on the rearrangement was also studied

The potassium and sodium alkoxides of 3-methyl-1,5-hexadien-3-ol follow first-order kinetics in the process of undergoing the anionic oxy-Cope rearrangement in tetrahydrofuran (THF) and dimethyl sulfoxide (DMSO). The isotope effects indicate a highly dissociative transition state with substantial bond breaking of the C3-C4 bond and little bond making between the allylic termiuni (C1 and C6+). The effects of aggregation and ionic dissociation are discussed in the context of mechanistic pathways proposed for the rearrangement in THF and in DMSO

Thermal oxy-Cope rearrangement of 1,2-divinylcycloalkanols led to ring expansion–cyclopentane annulation; the effect of ring size on the reaction has been studied.

Thermal oxy-Cope rearrangement of substrates 5,7 and 11 resulted in ring expansion and annulation. The effect of alkene substituents and variation in the ring systems on the reaction has been studied.

The unsaturated alcohols derived from a ‘one-pot’ tandem [2,3]-Wittig-anionic oxy-Cope (AOC) rearrangement undergo a halocyclisation reaction with iodine in acetonitrile to give substituted tetrahydropyrans with a high degree of stereocontrol.

The carbinol acetals 2a-h obtained by 1,2-addition of propargylmagnesium bromide to acyclic α-oxoketene dithioacetals 1a-h undergo cycloaromatization in the presence of trimethyl borate/methanol to give 2,5-bis(alkylthio)biphenyls 4a-henic oxy-Cope rearrangement and an unprecedented 1,4-alkylthio shift in the resulting allenic intermediate.

The aromatic oxy-Cope rearrangement including a benzene ring took place when 1-methoxy-2-aryl-bicyclo[2.2.2]oct-5-en-2- exo -ols and 2-(2-methoxyphenyl)-bicyclo[2.2.2]oct-5-en- exo -2-ols were treated with KH in THF.

Compounds containing a 1,5-hexadien-3-ol system undergo anionic oxy-Cope rearrangement when treated with the phosphazene super-base, P 4 - t -Bu. The [3,3] sigmatropic rearrangement occurs in hexane as well as in THF. The weaker phosphazene base, P 2 -Et fails to induce rearrangement. This is the first example of the use of a metal-free base to induce anionic oxy-Cope rearrangement.

[(6-Methyl-1-oxa-4-thiaspiro[4.5]dec-6-en-7-yl)(allyl)methanols were subjected to anion-accelerated oxy-Cope rearrangement in solvents such as THF, benzene and DME to assess the π-facial selectivity caused by the acetal function. The diastereomeric pairs 17a and 17b (R = Ph) furnished the same two diastereomeric products 18a and 18b, differing only in the relative preponderance. The reaction of 17a turned from mostly syn to oxygen (18a∶18b = 1∶4) in THF to moderately syn to sulfur (18a∶18b = 2.2∶1) in DME. The reaction was completely nonselective in benzene. The effect of solvent on the reaction of 17b was even more interesting. The reaction turned from completely nonselective (18a∶18b = 1∶1) in THF to highly syn to sulfur (18a∶18b = 5.4∶1) in DME. The selectivity in benzene was somewhere in between (18a∶18b = 2.7∶1). Likewise, the reaction of 17b (R = H) turned from moderately syn to oxygen in THF (18a∶18b = 1∶2) to nearly nonselective in DME (18a∶18b = 1∶1.1). The rotation around the bond between the methanol carbon and the adjacent ring-carbon is restricted to allow rearrangement only syn to sulfur in 17a and syn to oxygen in 17b. The considerable erosion in the observed diastereoselectivity is due to a radical and/or ionic retroaldol–recombination process. The radical pathway, however, is more prevalent than the ionic alternative. The recombination favors somewhat the addition of the allyl radical to the cogenerated 7-benzoyl-6-methyl-1-oxa-4-thiaspiro[4.5]dec-6-ene on the face syn to the sulfur. As a result of such dissociation and recombination, the oxy-Cope rearrangement does not appear suitable as a probe for the study of diastereofacial selectivity.

Racemic β-hydroxycyclohexanones with up to three chiral centres have been synthesized in a stereocontrolled way using the novel anionic oxy-Cope (AOC) rearrangement of acyclic enol ethers. The first examples of compounds containing an aldehyde and an enol ether in a 1,5 relationship are reported. Stereocontrol in the cyclisation of these compounds by a 6-(enolendo)-exo-trig intramolecular aldol reaction has been studied: there is high stereoselectivity for an axial hydroxy group in the product β-hydroxycyclohexanones. AM1 calculations show that there is a stabilising electrostatic attraction between the oxygen atom of the axial C-3 hydroxy group and the electron-poor carbon at C-1 in the intermediate oxonium ions. ≥87% of AOC rearrangement occurs via a chair-like transition state giving rise to the 5,6-anti stereochemistry of the β-hydroxycyclohexanones. Trapping the enolate product of AOC rearrangement with oxygen gives fragmentation via a 1,2-dioxetane.

Compounds containing a 1,5-hexadien-3-ol system undergo anionic oxy-Cope rearrangement when treated with the phosphazene super-base, P 4 - t -Bu. The [3,3] sigmatropic rearrangement occurs in hexane as well as in THF. The weaker phosphazene base, P 2 -Et fails to induce rearrangement. This is the first example of the use of a metal-free base to induce anionic oxy-Cope rearrangement.

The potassium and sodium alkoxides of 3-methyl-1,5-hexadien-3-ol follow first-order kinetics in the process of undergoing the anionic oxy-Cope rearrangement in tetrahydrofuran (THF) and dimethyl sulfoxide (DMSO). The isotope effects indicate a highly dissociative transition state with substantial bond breaking of the C3-C4 bond and little bond making between the allylic termiuni (C1 and C6+). The effects of aggregation and ionic dissociation are discussed in the context of mechanistic pathways proposed for the rearrangement in THF and in DMSO

We report the first instance where 1,2-dinaphthyl-1,2-diols of benzil and biacetyl undergo aromatic dianionic oxy-Cope rearrangement where the x bonds of the two naphthyl rings form the 1,5-hexadiene system necessary for oxy-Cope rearrangement.

A general synthesis of trans bicyclic carbinols with an angular methyl substituent using the anionic oxy-Cope rearrangement is reported. The carbinols 13a , l3b , 14a , 14b and 15 furnish the bicyclic carbinols 16a , 16b 17a , 17b and 18 when treated with potassium hydride in 1,2-dimethoxyeth ane.

Treatment of dinaphthyl diols of 1,10‐phenanthroline (1) and acenaphthene (2) with nonnucleophilic base gave bicyclic ketones (3) and (4), respectively. The formation of (3) and (4) involves aromat...

Novel anionic oxy-Cope (AOC) rearrangements of substituted 5-alkylthio-1,5-dien-3-ols were studied. Aqueous quench gave new access to compounds with a nucleophilic vinyl sulfide and an electrophilic aldehyde in a 1,5 relationship. 3,4-Anti and 3,4-syn 1E,5Z-5-hexylthio-4-methyl-1-phenylhepta-1,5-dien-3-ols were synthesised separately by stereoselective aldol reaction, thioesterification and alkylidenation of the resulting thioesters to give Z-vinyl sulfides with ⩾90% stereoselectivity. AOC rearrangement of the 3,4-syn substrate gave predominantly 3,4-syn Z-vinyl sulfide while the 3,4-anti substrate gave mostly 3,4-syn E-vinyl sulfide, via chair-like transition states with the oxyanion pseudo-equatorial. Stereochemistry was assigned by NOE taking advantage of the conformational stability of the products.

Treatment of 5-bromopenta-1,3-diene with indium metal in the presence of α,β-unsaturated ketones results in initial γ-penta-dienylation to generate the hydroxy-1,4-diene. In the case of aromatic conjugated ketones or cyclohexenones the indium alkoxide undergoes spontaneous oxy-Cope rearrangement to afford the 1,4-addition product. The second double bond is required for this [3,3] sigmatropic rearrangement as allyl groups fail to under go this in situ rearrangement. This behavior is consistent with an indium(I) pentadiene species and appears to be the first example of an indium-mediated oxy-Cope rearrangement.

Treatment of 1,6-dialkylhexa-1,5-diene-3,4-diones with bis(iodozincio)methane at −78 °C for several hours gave cis-dialkenylcyclopropane-1,2-diols which rearranged into the zinc alkoxides of cis-5,...

Synthese de derive de cyclopropa benzo [a] azulene a partir de dimethyl-7,7 methoxy-4 norcaranone-3, de chloro-2 cyclohexanone et de bromure de vinyl magnesium