Regioselective and asymmetric allylic alkylation of vinyl epoxides for the construction of allylic alcohols via synergistic catalysis

A highly efficient asymmetric allylic alkylation of cyclic and acyclic carbon nucleophiles with vinyl epoxides has been developed,which exhibits good functional group compatibility,high atomic and step economy.This protocol utilizes a strategy of synergistic catalysis with a chiral N,N’-dioxide/Ni^Ⅱ complex and an achiral Pd⁰ catalyst,generating a series of multisubstituted allylic alcohols with a quaternary carbon stereocenter in high yield and excellent regio-,Z/E-and enan...     

Cp2TiCl-promoted isomerization of trisubstituted epoxides to exo-methylene allylic alcohols on carvone derivatives

The ring-opening reaction of trisubstituted epoxides promoted by Cp2TiCl led to exo-methylene allylic alcohols as major compounds when 0.5 M solutions of the epoxides were added to 0.1 M solutions of the reagent at room temperature in THF. In most cases, the allylic alcohols were contaminated with saturated alcohols. Normal and reverse addition modes led to the alternate product being favored. The different stereochemical outcome of cis- and trans-epoxy acetates is rationalized in terms of mechanistically biased elimination processes.     

A versatile new catalyst for the enantioselective isomerization of allylic alcohols to aldehydes: scope and mechanistic studies.

A new planar-chiral bidentate phosphaferrocene ligand (2) has been synthesized and structurally characterized. The derived rhodium complex, [Rh(cod)(2)]BF(4), serves as an effective catalyst for asymmetric isomerizations of allylic alcohols to aldehydes, furnishing improved yields, scope, and enantioselectivities relative to previously reported methods. The catalyst is air-stable and can be recovered at the end of the reaction. Mechanistic studies establish that the isomerization proceeds via an intramolecular 1,3-hydrogen migration and that the catalyst differentiates between the enantiotopic C1 hydrogens.     

Asymmetric Catalysis by Vitamin B12. The isomerization of achiral epoxides to optically active allylic alcohols

Achiral epoxides are isomerized to optically active allylic alcohols under the influence of catalytical amounts of cob(I) alamin in protic polar solvents.     

Catalytic asymmetric cyclopropanation of allylic alcohols with titanium-TADDOLate: scope of the cyclopropanation reaction.

A substoichiometric amount of titanium-TADDOLate complex was effective at catalyzing the cyclopropanation reaction of allylic alcohols in the presence 1 equiv of bis(iodomethyl)zinc. After initial optimization of the catalyst structure, excellent yields and enantiomeric ratios were obtained for 3-aryl- or 3-heteroaryl-substituted allylic alcohols (up to 97:3). Alkyl-substituted allylic alcohols gave modest yields and enantiomeric ratios (up to 87:13) but these compare favorably with those observed with other substoichiometric chiral ligands. The full synthetic scope of the reaction is presented in this paper.     

Isomerization of epoxides to allylic alcohols using methylmagnesium N-cyclohexylisopropylamide

The scope of methylmagnesium N-cyclohexylisopropylamide promoted isomerizations of epoxides to allylic alcohols Is described.     

CpRu(PN) complex-catalyzed isomerization of allylic alcohols and its application to the asymmetric synthesis of muscone

Highly efficient isomerization of allylic alcohols into saturated carbonyls is accomplished using the catalyst system of Cp*RuCl[Ph2P(CH2)2NH2-kappa2-P,N]-KOt-Bu (Cp* = eta5-C5(CH3)5) under mild conditions. Mechanistic consideration based on isotope-labeling experiments indicated the present reaction is applicable to the asymmetric isomerization of racemic sec-allylic alcohols with a prochiral olefin via dynamic kinetic resolution. A concise asymmetric synthesis of muscone has been achieved, where the asymmetric isomerization using an optically active ligand is a key reaction.     

Synthesis of allylic alcohols via organopalladium additions to unsaturated epoxides

The reaction of aryl- and vinylpalladium compounds with vinylic and allylic epoxides provides an excellent, high yielding, regio- and stereoselective route to functionally substituted allylic alcohols which can be made catalytic in palladium.     

Novel catalytic kinetic resolution of racemic epoxides to allylic alcohols

[formula: see text] The kinetic resolution of racemic epoxides via catalytic enantioselective rearrangement to allylic alcohols was investigated. Using the Li-salt of (1S,3R,4R)-3-(pyrrolidinyl)methyl-2-azabicyclo [2.2.1] heptane 1 as catalyst allowed both epoxides and allylic alcohols to be obtained in an enantioenriched form.     

Electrocremical procedure directed to the selective ring opening of epoxides to allylic alcohols

A transformation of epoxides $\text{2}$ into allylic alcohols $\text{1}$ was achieved by an electrogenerated acid-catalysis in a ClCH₂CH₂Cl - TsONa - TsONEt₄ -Pt system.     

Palladium-diphosphite catalysts for the asymmetric allylic substitution reactions

[structure: see text] We have designed a series of diphosphite ligands to study the effect of the backbone, the size of the chelate ring, and the substituents of the biphenyl moieties and to determine the scope of this type of ligand in the Pd-catalyzed asymmetric substitution reactions of different types of substrates. Good-to-excellent activities and enantioselectivities have been obtained for disubstituted linear substrate 11 (TOF's up to >2000 mol x (mol x h)(-1), ee values up to 99%) and cyclic substrate 14 (TOF up to 285 mol x (mol x h)(-1), ee values up to 92%). However, these ligands are inadequate for the Pd-catalyzed allylic alkylation of monosubstituted linear substrates because they provide low enantioselectivities.     

Catalytic asymmetric rearrangement of allylic N-aryl trifluoroacetimidates. A useful method for transforming prochiral allylic alcohols to chiral allylic amines

[reaction: see text] A useful method for the conversion of prochiral allylic alcohols to chiral allylic amines of high enantiopurity is reported. N-(4-Methoxyphenyl)trifluoroacetimidates are excellent substrates for the palladium(II)-catalyzed allylic imidate rearrangement as the allylic trifluoroacetamide products can be deprotected in two steps to provide chiral nonracemic allylic amines. Di-mu-chlorobis[(eta(5)-(S)-(pR)-2-(2'-(4'-isopropyl))oxazolinylcyclopentadienyl,1-C,3'-N))(eta(4)-tetraphenylcyclobutadiene)cobalt]dipalladium (6a, COP-Cl) is a superior catalyst because it does not require activation with silver salts and provides rearranged allylic trifluoroacetamides in good yields and high enantiomeric purities.     

Scope and limitations of the catalytic asymmetric rearrangement of epoxides to allylic alcohols using chiral lithium amide bases/lithiated imidazoles

The catalytic asymmetric rearrangement of functionalised cyclohexene and cyclopentene oxides has been studied using sub-stoichiometric amounts of a chiral lithium amide in combination with a stoichiometric amount of three different lithiated imidazoles. 1-Methylimidazole that had been lithiated at the C-2 aryl position gave the highest enantioselectivity (82% ee). With 1,2-dimethylimidazole that had been lithiated at the C-2 methyl group, epoxide ring opening occurred as an unexpected and competing process. Ultimately, ring opening was suppressed using a more sterically hindered imidazole. In all catalytic examples, a racemic background reaction (presumably due to rearrangement by the lithiated imidazoles) was observed.     

Structural and solvent effects on the mechanism of base-induced rearrangement of epoxides to allylic alcohols

A combined experimental and computational study is presented which explores the influence of structure and solvent on the base-catalyzed isomerization of cyclopentene- and cyclohexene oxides. Cyclohexene oxide is known to rearrange via a syn beta-elimination in nonpolar solvents. Cyclopentene oxide instead undergoes alpha-elimination to a carbenoid intermediate in nonpolar solvents due to the unusual acidity of the alpha-proton, not because of an unfavorable conformation. In HMPA, cyclopentene oxide undergoes beta-elimination. To explore the origins of this mechanistic change, deuterium-labeled cis-4-tert-butylcyclohexene oxide was rearranged in HMPA and was found to react via anti beta-elimination, as presumably do cyclopentene oxide and other epoxides.     

Copolymers of polystyrene—New polymer supports for asymmetric epoxidation of allylic alcohols

Tartrate‐functionalized polystyrene copolymers were prepared with divinyl benzene, tetraethyleneglycol diacrylate, and diallyl tartrate as the crosslinking agents. These insoluble materials possessed the unique advantages of heterogeneous reagents. These resins were used to support the asymmetric epoxidation of allylic alcohols along with titanium tetraisopropoxide and tert‐butyl hydroperoxide with reasonably good yields and a high enantiomeric excess. The swelling behavior and molecular architecture of the polymer backbone significantly influenced the effectiveness of the catalyst. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 161–169, 2000     

Reactions of 2,3-epoxyhalides. Synthesis of optically active allylic alcohols and homoallylic epoxides

Mild and efficient reactions for the conversion of optically active 2,3-epoxy-halides to optically active allylic alcohols and optically active epoxides are described.     

Metal oxo complexes as catalysts for the isomerisation of allylic alcohols

The 1,3-allylic rearrangement of allylic alcohols is an important transformation in organic synthesis and various methods for effecting such a transposition have been reported. This short review will focus on the development of transition metal oxo complexes as catalysts for the isomerisation of allylic alcohols. Mechanistic investigations are also discussed.     

Rhenium-catalyzed 1,3-isomerization of allylic alcohols: scope and chirality transfer

The scope of the triphenylsilyl perrhennate (O3ReOSiPh3, 1) catalyzed 1,3-isomerization of allylic alcohols has been thoroughly explored. It was found to be effective for a wide variety of secondary and tertiary allylic alcohol substrates bearing aryl, alkyl, and cyano substituents. Two general reaction types were found which gave high levels of product selectivity: those driven by formation of an extended conjugated system and those driven by selective silylation of a particular isomer. The efficiency of chirality transfer with various substrates was investigated, and conditions were found in which secondary and tertiary allylic alcohols could be formed with high levels of enantioselectivity. Consideration of selectivity trends with respect to the nature of the substituents around the allylic system revealed that this is a reliable and predictable method for allylic alcohol synthesis.