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.     

Catalytic regiodivergent kinetic resolution of allylic epoxides: a new entry to allylic and homoallylic alcohols with high optical purity

A novel regiodivergent kinetic resolution of a series of allylic epoxides with alkylzinc reagents is described. Results demonstrate the potential of chiral copper-phosphoramidite catalysts for enantiomer differentiation of allylic epoxides, allowing a chiral catalyst-stereoregulated synthesis of cyclic allylic and homoallylic alcohols with high optical purities.     

Part I. epoxydes diterpeniques : synthese et reactivite d'epoxydes derives d'acides resiniques

Epoxidation of methyl esters of resin acids with the pimarane skeleton with p-nitroperbenzoic acid has permitted the isolation of epoxides of the intracyclic double bond. Allylic diterpenic alcohols were obtained by acid-catalysed isomerisation of diterpene epoxides, and the action of Collins reagent on these allylic alcohols has been studied.     

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.     

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.     

Mixed disproportionation versus radical trapping in titanocene(III)-promoted epoxide openings

The formation of either deoxygenation products or allylic alcohols from epoxides is observed when these substrates are treated with Cp₂TiCl under anhydrous conditions. It seems that processes via trisubstituted radicals give allylic alcohols whereas processes via disubstituted radicals may give deoxygenation products or allylic alcohols depending on the structure of the original epoxide. This method allows a controlled access to these functional groups, providing a useful tool in organic synthesis. A mechanistic discussion for these transformations is reported.     

Diastereoselective Weitz-Scheffer epoxidation of levoglucosenone for the synthesis of isolevoglucosenone and derivatives

High-yielding epoxidation conditions for the cellulose pyrolysis product (?)-levoglucosenone (LGO) and 3-aryl derivatives of LGO have been developed. The reaction of LGO with hydrogen peroxide/base is known to give a Baeyer-Villiger reaction, however, it was found that the reactions of LGO or derivatives with tert-butylhydroperoxide/base affords solely epoxides through the Weitz-Scheffer reaction. A critical parameter in the successful isolation of the epoxide from LGO was to avoid all contact with water or alcohols during the reaction and workup. The epoxide products were reacted under Wharton conditions affording allylic alcohols and subsequent oxidation led to isolevoglucosenone or 3-arylisolevoglucosenone derivatives. Previously unreported reactions on isolevoglucosenone were then investigated.     

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.     

A practical one-pot radical-ionic sequence for the preparation of epoxides: application to the synthesis of unnatural polyhydroxylated alkaloids

An efficient one-pot sequence for the preparation of epoxides from α-iodoesters or α-iodonitriles and allylic alcohols is described. This sequence is based on the use of iodine atom transfer reaction onto allylic alcohols followed by a ring closing epoxidation reaction of the halohydrin intermediates. The feasibility of this sequence is showcased in the synthesis of the perhydroaza-azulene, an unnatural analog of castanospermine.     

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.     

Asymmetric base-mediated epoxide isomerisation

The base-mediated rearrangement of epoxides into allylic alcohols is a well-known synthetic transformation. The first enantioselective version of the reaction using a chiral base was reported in 1980. Since then, the reaction has received a lot of attention mostly due to the great usefulness of chiral allylic alcohols in organic synthesis. Major breakthroughs in the area were the first report on using a sub-stoichiometric amount of chiral base, and the development of chiral bases for a true catalytic reaction protocol. The present review covers the time from when the first asymmetric epoxide isomerisation reaction was reported (1980) up to now, focusing on the period 1997-2001.     

Reactivite des epoxydes—II: Influence du milieu reactionnel lors de l'ouverture des epoxydes par les amidures de lithium

The suppression of α-elimination during opening of epoxides by lithium amides (RRNLi) is possible by the use of HMPT as a solvent. This solvent effect is general and is of some interest for the preparation of allylic alcohols by epoxides opening with lithium amides. Formation of by-products such as ketones or aminoalcohols is also avoided in this polar solvent.     

A regio- and stereodivergent route to all isomers of vic-amino alcohols

Vicinal amino alcohols are substructures in several important natural products. They are also frequently employed ligands in asymmetric synthesis. Many enantioselective syntheses of vic-amino alcohols have been reported, but each structure has required its own synthetic route. This study presents a synthetic strategy leading to all eight possible isomers of a given beta-amino alcohol, starting from vinyl epoxides. The developed strategy focuses on the propensity of vinyl epoxides and vinylaziridines to be selectively ring-opened at the allylic position by suitable hard nucleophiles. Within this strategy, a novel large-scale aminolysis reaction and the synthesis of a trisubstituted N-H vinylaziridine are detailed.     

Regioselectivity of olefin oxidation by iodosobenzene catalyzed by metalloporphyrins : control by the catalyst

The regioselectivity of the oxidation of three monosubstituted olefins, 6-phenoxyhex-1-ene, hex-1-ene and styrene, by iodosobenzene in the presence of various Fe-, Mn- or Cr-tetraaryl-porphyrins, was studied. It was found that, besides epoxides, known products from such systems, allylic alcohols and aldehydes were formed, the latter not being derived from the corresponding epoxides. The relative importance of these reactions greatly depends upon both the metal and porphyrin constituents of the catalyst. More particularly, the competition between epoxidation and allylic hydroxylation can be efficiently controlled by non-bonded interactions between the olefin and porphyrin substituents. No hydroxylation of the aromatic rings and no oxidative dealkylation of the ether function was detected.     

Reactivite du tetraallyletain et d'allyltrialkyletains vis a vis d'aldehydes,de cetones et d'epoxydes

Tetraallytin reacts readily with non activated ketones and exothermically with aldehydes contrary to other allylic organotins such as allytributyltin. Homoallylic alcohols are obtained after acidolysis of the adducts. Upon extended heating, allylic organotins and epoxides form products which correspond to additon products of isomeric carbonyl compounds. However, starting from cis- and trans-1-phenyl-1,2-epoxypropanes, direct regiospecific but non-stereospecific ring opening is observed with poor yields.     

Enantioselective epoxidation with chiral MN(III)(salen) catalysts: kinetic resolution of aryl-substituted allylic alcohols

A set of aryl-substituted allylic alcohols rac-2 has been epoxidized by chiral Mn(salen*) complexes 1 as the catalyst and iodosyl benzene (PhIO) as the oxygen source. Whereas one enantiomer of the allylic alcohol 2 is preferentially epoxidized to give the threo- or cis-epoxy alcohol 3 (up to 80% ee) as the main product (dr up to >95:5), the other enantiomer of 2 is enriched (up to 53% ee). In the case of 1,1-dimethyl-1,2-dihydronaphthalen-2-ol (2c), the CH oxidation to the enone 4c proceeds enantioselectively and competes with the epoxidation. The absolute configurations of the allylic alcohols 2 and their epoxides 3 have been determined by chemical correlation or CD spectroscopy. The observed diastereo- and enantioselectivities in the epoxidation reactions are rationalized in terms of a beneficial interplay between the hydroxy-directing effect and the attack along the Katsuki trajectory.     

Formation of dihydroxyselenides from allylic alcohols and their conversion to β-hydroxy epoxides via substitution of a phenylselenonyl group

Hydroxyselenation of allylic alcohols occurs with high regio- and stereoselectivity to give β,β′-dihydroxyphenylselanyl adducts in high yields. An exception is the reaction of the terminal alcohol, 2-methylprop-2-en-1-ol, which forms only a 1,2-diol product. Generally, the addition is Markovnikov in orientation, but the fact that one anti-Markovnikov addition is observed and that addition to 1,2-disubstituted alkenes shows a strong preference for one regioisomer suggests that an interaction of the allylic alcohol with the selenium atom of the reaction intermediate (which weakens the C_β-Se bond in the intermediate) is also an important factor in determining the preference for addition of the phenylselanyl group to the double bond carbon nearest the allylic alcohol. The hydroxyselenated adducts of allylic alcohols can be readily converted to β-hydroxy epoxides in good yields via oxidation with m-chloroperbenzoic acid to a selenone and subsequent treatment with base. Hydroxyselenation of crotyl acetate and 3-acetoxycyclohexene is more regiocatholic than hydroxyselenation of the corresponding allylic alcohols. It appears that the known selectivity of additions of phenylselanyl chloride to these acetates in organic solvents is lost when water or a Lewis acid complexes to the acetate group.     

A novel synthesis of epoxides and allylic alcohols from carbonyl compounds through α, β-epoxy sulfoxides

Treatment of α,β-epoxy sulfoxides, easily prepared from carbonyl compounds with 1 equivalent of n-butyllithium at −100 °C gave the desulfinated epoxides in good yields. The similar α,β-epoxy sulfoxides having arylmethyl group at α-position, on treatment with excess n-butyllithium at −70 °C afforded 3-aryl allylic alcohols.     

New Nitrogen,Sulfur-, and Selenium-Donating Ligands Derived from Chiral Pyridine Amino Alcohols. Synthesis and Catalytic Activity in Asymmetric Allylic Alkylation

Although many chiral ligands for asymmetric catalysis have been developed, there is still a need for new structures allowing the modular approach. Recently, easy synthesis of chiral pyridine-containing β-amino alcohols has been elaborated by opening respective epoxides with enantiomeric 1-phenylethylamine. This paper reports the synthetic transformation of β-amino alcohols into the new complexing pyridine-containing seleno- and thioethers. The amino alcohols were effectively converted to cyclic sulfonamidates, which were reacted with thiolates or phenyl selenide nucleophile. The reaction was diastereoselective, and its outcome depended on the configuration at the substitution center. The problem was discussed considering DFT optimized structures of both diastereomeric sulfonamidates. New amino-aldimine ligands were also synthesized from chiral pyridine-containing diamines. Nine new chiral ligands were tested in the Tsuji-Trost allylic alkylation resulting in the enantiomerically enriched product in up to 75% ee. The observed stereochemical induction agrees with the prevailing nucleophilic attack at the allylic carbon laying opposite to the complexing nitrogen of pyridine in η³-allylic intermediate complexes.     

Palladium-catalyzed reactions of hypophosphorous compounds with allenes, dienes, and allylic electrophiles: methodology for the synthesis of allylic h-phosphinates

Hypophosphorous compounds (MOP(O)H(2), M = H, R(3)NH) effectively participate in metal-catalyzed C-P bond-forming reactions with allenes, dienes, and activated allylic electrophiles under mild conditions. The catalytic system Pd(2)dba(3)/xantphos is crucial to avoid or minimize the competitive reductive transfer-hydrogenation pathway available to hypophosphorous acid derivatives. Further investigation into the allylation mechanism provided access to the analogy allylic acetate-allylic phosphinate, which then led to the development of a Pd-catalyzed rearrangement of preformed allylic phosphinates esters and, ultimately, to a catalytic dehydrative allylation of hypophosphorous acid with allylic alcohols. The reactions disclosed herein constitute efficient synthetic approaches, not only to prepare allylic H-phosphinic acids but also their esters via one-pot tandem processes. In addition, the potential of H-phosphinates as useful synthons for the preparation of other organophosphorus compounds is demonstrated.