Anionic oxy-Cope Research Articles

Intramolecularly competitive anionic oxy-cope rearrangements

Two examples of the title reaction are described. While the kinetically preferred pathway for 2 utilizes the vinyl substituent, that for 16 skirts this option completely. To a great extent, these biases are a function of the structural features inherent to these alochols.

Application of the Anionic Oxy-Cope Rearrangement to Stereocontrolled Synthesis of the A/B Subunit of Cytoxic 8,9-Seco-ent-kaurenes

Methodology is described for expedient synthesis of the A/B framework of 8,9-seco-ent-kaurenes and for introduction of the 5-methylene-2-cyclopentenone moiety. In the first part of the study, a sequence of only six steps is necessary to convert 2-(hydroxymethylene) cyclohexanone to a key functionalized intermediate. Five of the transformations are 100% stereocontrolled as a direct result of complementary steric biases that operate in the desired direction. The final target is arrived at by selective protection/oxidation of the oxygenated centers. This first synthetic entry to the structural core of the titled diterpenes is expected to guide the future de novo acquisition of these cytotoxic agents.

Acyclic diastereocontrol and asymmetric transmission via anionic oxy-Cope rearrangement: a synthetic application of sequential [2,3]Wittig-oxy-Cope rearrangements

Acyclic diastereocontrol and asymmetric transmission via anionic oxy-Cope rearrangement: a synthetic application of sequential [2,3]Wittig-oxy-Cope rearrangements

Importance of Oxyanion Orientation to the Stereochemical Control of Anionic Oxy‐Cope Rearrangements

The enantiomerically pure alcohols 1 and 2 react in an anionic oxy-Cope rearrangement to afford mixtures of (S)- and (R)-4-methyl-5-hexenal(3 and ent-3, respectively). The findings demonstrate that transition states with the oxido group in equatorial position are not as favored in acyclic systems as previously assumed. The oxido group occupies an axial position in 36–40% of the transition states.

Thermal reactions of a 2-aryl-1-vinylcyclobutanol

Thermolysis reactions of the exo (distal) and endo (proximal) isomers of 7-vinyl-6b,8,8a-tetrahydrocyclobut[a]acenaphthylen-7-ol ( 1a and 1b) have been studied, both in refluxing xylene and in a packed pyrolysis column. These epimers were prepared from the corresponding cyclobutanone ( 3). An oxy-Cope rearrangement of 1b was not observed under any conditions. Both epimers gave the same thermolysis products, a fused cyclohexanone derivative 15 (a formal [1,3] shift product) and vinyl ketone 16 (a retro-ene product). At temperatures above 250 °C some acenaphthylene was also obtained. The anionic oxy-Cope variant gave only 15. A common diradical intermediate is proposed for the thermal reactions.

Impact of substituent modifications on the atropselectivity characteristics of an anionic oxy-Cope ring expansion

The phenomenon of atropisomerism is critically examined in the tricyclic E, syn, up enolates derived from anionic oxy-Cope rearrangement of 1-vinyl-2-cyclohexenyl-7,7-dimethyl-exo-norbornan-2-ols, as well as the ketones derived from their protonation and methylation. In all cases studied, the [3,3] sigmatropic shift proceeds with 100% stereoselectivity via the endo-chair transition-state option. The E and syn stereochemistry is established during chirality transfer at this stage. The «oxygen-up» conformation stems directly from the structural features inherent in the starting alcohols. In the unsubstituted example and with certain substitution pattrerns in the original cyclohexene ring, the E, syn, up enolates are seen to be thermodynamically unstable relative to their E, syn, down atropisomers, such that products results exclusively by electrophilic capture of the latter. By suitable substitution, the barrier to this preequilibrium can be sufficiently heightened so that products resulting from the E, syn, up species can be obtained

Acyclic Oxy-Cope Rearrangement. Dependence of E/Z Stereoselection on Substrate Stereochemistry

Abstract The E/Z stereoselection in the acyclic oxy-Cope rearrangement of stereochemically-defined 3-methyl-1,5-heptadien-4-ols, prepared via diastereoselective [2,3]Wittig variants, has been evaluated, thereby permitting to propose a reasonable transition-state model for this type of anionic oxy-Cope variant.

A stereocontrolled intramolecular cycloaddition – sigmatropic rearrangement approach to a tricyclo[7.4.01,6.01,10]tridecane precursor for (±) gascardic acid

A general intramolecular Diels–Alder anionic oxy-Cope strategy for the synthesis of tricyclic skeletons and its application to the preparation of the gascardic acid precursor 21 is described. In situ generation of the appropriate cyclopentadiene 9 by isomerization (Et3N) afforded the [4+2] adduct directly or with EtAlCl2 as catalyst. The requisite potassium salt of the 1,5 diene 16 rearranged with concomitant epimerization at 67 °C to the fused ring ketone 18. Selective allylic oxidation and reduction provided 21. Key words: Diels–Alder, oxy-Cope, sesterterpene, synthesis, cycloaddition.

ChemInform Abstract: New Synthesis of Angularly Substituted Bicyclic Systems via an Anionic Oxy‐Cope Rearrangement.

AbstractA general synthesis of trans bicyclic carbinols (V) with an angular methyl substituent uses the anionic oxy‐Cope rearrangement of the precursors (III).

A Facile Entry into Bicyclo[3.3.0] Octene System Via Anionic Oxy-Cope Rearrangement

Abstract The bicyclo[3.3.0] octene system has been synthesised from the readily available starting material 2-methyl-cyclohexane-1,3-dione, utilizing the base catalysed oxy-Cope rearrangement as a key step.

ChemInform Abstract: Direct Oxygenation of Enolates Generated by Anionic Oxy‐Cope Rearrangement. Expedient Preparation of Polycyclic α‐Hydroxy Ketones.

AbstractReaction of the ketones (I), (VI), and (XI) with vinylmetallic agents yields the allyl vinyl carbinols (III), (VIII), and (XIII) respectively.

Sequential vinylcyclopropylcarbene and anionic oxy-cope rearrangements: An expedient synthesis of nine-membered rings

5-Alkenyl-2-methoxy-2-cyclopentenones, readily available from thermolysis of 2-alkenylcyclopropylcarbene-chromium complexes, can be converted to nine-membered rings by treatment with vinylcerium reagents and subsequent anionic oxy-Cope rearrangement.

Boat/chair topographic stereoselection during anionic oxy-Cope rearrangement of 1-alkenyl-2-cyclopentenyl-endo-norbornan-2-ols

Boat/chair topographic stereoselection during anionic oxy-Cope rearrangement of 1-alkenyl-2-cyclopentenyl-endo-norbornan-2-ols

Enantiocontrolled synthesis of quaternary carbon centers via anionic oxy-Cope rearrangement: an efficient synthesis of (+)-dihydromayurone

Synthese de dihydromayurone a partir de β-cyclocitral. L'etape de la synthese est une transposition anionique oxy-Cope de trimethyl-2',2',6' cyclohexene-1'yl-1 butene-3ol-2 en trimethyl-1,3,3 methylene-2 cyclohexanepropanal

A new synthesis of angularly substituted bicyclic systems via an anionic 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.

Synthetic Stuides on Nine-membered Ring Diterpenoids: Stereoselective Construction of Optically Active 1-Oxaspiro[2.8]undecenone Derivatives

Enantiomeric isomers of 1-oxaspiro[2.8]undecone derivative (10), which are key compounds to synthesize nine-membered ring diterpenoids, were synthesized stereoselectivity from optically active monoterpene, limonene, via anionic oxy-Cope rearrangement reaction

Stereocontrolled construction of hydroazulenones by sequential anionic oxy-Cope rearrangement - SN' allylic ether displacement

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

Direct oxygenation of enolates generated by anionic oxy-Cope rearrangement. Expedient preparation of polycyclic .alpha.-hydroxy ketones

Direct oxygenation of enolates generated by anionic oxy-Cope rearrangement. Expedient preparation of polycyclic .alpha.-hydroxy ketones

ChemInform Abstract: Limitations in the Application of Anionic Oxy‐Cope Sigmatropy to Elaboration of the Forskolin Nucleus.

AbstractThe bicyclooctenone (II) undergoes 1,2‐addition with lithiated dihydropyran (III) to give the alcohols (IV) and (V).

ChemInform Abstract: 5,6‐Dehydrocamphor: A Chiral Intermediate in Terpenoid Synthesis.

Abstract(+)‐endo‐3‐Bromocamphor (I) rearranges upon treatment with chlorosulfonic acid, forming (‐)‐endo‐6‐bromocamphor (II).