Renewable camphor-derived hydroperoxide: synthesis and use in the asymmetric epoxidation of allylic alcohols

Renewable enantiopure tertiary furyl hydroperoxide has been easily synthesized in two steps starting from low cost (+)-(1R)-camphor and it has been used in the asymmetric epoxidation and kinetic resolution of allylic alcohols (enantioselectivities up to 46%).     

Nanosheet-enhanced enantioselectivity in the vanadium-catalyzed asymmetric epoxidation of allylic alcohols

The use of suitable chiral ligands is an efficient means of producing highly enantioselective transition-metal catalysts. Herein, we report a facile, economic, and effective strategy for the design of chiral ligands that demonstrate enhanced enantioselectivity and catalytic efficacy. Our simple strategy employs naturally occurring or synthetic inorganic nanosheets as huge and rigid planar substituents for, but not limited to, naturally available α-amino-acid ligands; these ligands were successfully used in the vanadium-catalyzed asymmetric epoxidation of allylic alcohols. The crucial role of the inorganic nanosheets as planar substituents in improving the enantioselectivity of the reaction was clearly revealed by relating the observed enantiomeric excess with the distribution of the catalytic centers and the accessibility of the substrate molecules to the catalytic sites. DFT calculations indicated that the LDH layer improved the enantioselectivity by influencing the formation and stability of the catalytic transition states, both in terms of steric resistance and H-bonding interactions.     

Highly diastereo- and enantio-selective epoxidation of secondary allylic alcohols catalyzed by styrene monooxygenase

Enantiomerically enriched glycidol derivatives with contiguous stereogenic centers were obtained in a highly diastereo- and enantio-selective epoxidation catalyzed with the styrene monooxygenase StyAB2.     

Selective epoxidation of allylic alcohols with dibutyltin oxyperoxide

Dibutyltin oxyperoxide derived from Bu₂SnO and ^tBuOOH epoxidize allylic alcohols with high stereo- and regioselectivities.     

Highly selective, recyclable epoxidation of allylic alcohols with hydrogen peroxide in water catalyzed by dinuclear peroxotungstate

The highly chemo-, regio-, and diastereoselective and stereospecific epoxidation of various allylic alcohols with only one equivalent of hydrogen peroxide in water can be efficiently catalyzed by the dinuclear peroxotungstate, K2[[W(=O)(O2)2(H2O)]2(mu-O)].2H2O (I). The catalyst is easily recycled while maintaining its catalytic performance. The catalytic reaction mechanism including the exchange of the water ligand to form the tungsten-alcoholate species followed by the insertion of oxygen to the carbon-carbon double bond, and the regeneration of the dinuclear peroxotungstate with hydrogen peroxide is proposed. The reaction rate shows first-order dependence on the concentrations of allylic alcohol and dinuclear peroxotungstate and zero-order dependence on the concentration of hydrogen peroxide. These results, the kinetic data, the comparison of the catalytic rates with those for the stoichiometric reactions, and kinetic isotope effects indicate that the oxygen transfer from a dinuclear peroxotungstate to the double bond is the rate-limiting step for terminal allylic alcohols such as 2-propen-1-ol (1a).     

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     

An immobilized vanadium-binaphthylbishydroxamic acid complex as a reusable catalyst for the asymmetric epoxidation of allylic alcohols

An immobilized polymer-supported vanadium-binaphthylbishydroxamic acid (PS-VBHA) has been developed as an efficient, reusable catalyst for the asymmetric epoxidation of allylic alcohols. This PS-VBHA catalyst shows comparable catalytic performance to that of the parent V-BBHA catalyst and can be reused five times without significant loss of enantioselectivity.     

Enantioselective iminium-catalyzed epoxidation of hindered trisubstituted allylic alcohols

The reactivity of diastereomeric biaryl iminium cations made of a (Ra)-5,5′,6,6′,7,7′,8,8′-octahydrobinaphthyl core and exocyclic appendages derived from (S)- or (R)-3,3-dimethylbutyl-2-amine was investigated with hindered trisubstituted allylic alcohols—a class of alkenes which had not been previously studied in detail in epoxidation reactions with cyclic iminium catalysts (ee up to 98%). Surprisingly, generally strong matched/mismatched effects are observed not only in terms of reactivity but also on the enantioselectivity of the reaction (Δee up to 16%). Also, for the most hindered substrates, two sets of reaction conditions were tested in a preliminary study and little advantage was found in running reactions in MeCN/water instead of CH₂Cl₂/water/18-C-6. In any case, the presence of the hydroxyl group did not reveal any anchimeric effect.     

Highly efficient catalytic aerobic oxidations of benzylic alcohols in water

A highly efficient catalytic system without transition metals in water has been developed for aerobic oxidations of benzylic alcohols. The newly developed catalyst system could oxidize benzylic alcohols and heteroaromatic analogues with 1 mol % TEMPO as a catalyst and with a catalytic amount of 1,3-dibromo-5,5-dimethylhydantoin and NaNO2 as cocatalysts. Under the optimal conditions, various alcohols could be converted into their corresponding aldehydes or ketones in high yields.     

Direct catalytic azidation of allylic alcohols

A direct catalytic azidation of primary, secondary, and tertiary allylic alcohols has been developed. This new azidation reaction affords the corresponding allylic azides in high to excellent yields and regioselectivities. The reaction provides straightforward access to allylic azides that are valuable intermediates in organic synthesis, including the preparation of primary amines or 1,2,3-triazole derivatives.     

Palladium-catalyzed asymmetric umpolung allylation of imines with allylic alcohols

A palladium-catalyzed asymmetric umpolung allylation reaction of imines with allylic alcohols has been developed. In the presence of chiral spiro phosphoramidite ligand 4, the allylation was accomplished with high yields and good enantioselectivities. The use of highly stable and easily available allylic alcohols instead of allylic metal reagents facilitated the preparation of chiral homoallylic amines.     

Highly regioselective and diastereoselective epoxidation of allylic amines with Oxone

Allylic amines (as their protonated ammonium salts) can be epoxidised with high syn diastereoselectivity and regioselectivity at the proximal alkene in substrates with several double bonds using Oxone. The protonated ammonium cation activates the Oxone by hydrogen bonding, thus promoting the oxidation of groups within the vicinity of the complex.     

Further studies on stereospecific epoxidation of allylic alcohols Iltifat Hasan

A stereosepcific synthesis of the epoxides $\text{4}$ and $\text{12c}$ is described.     

Highly atom efficient catalytic reactions utilizing water and alcohols as reagents

In this accounts, we describe our recent studies on hydrolysis, alcoholysis, and addition of alcohols to organic molecules. The reactions utilizing water and alcohols as a reagent are one of the most basic and simple reactions. The palladium-catalyzed asymmetric hydrolysis and alcoholysis of vinyl ethers gave valuable axially chiral 1,1′-bi-2-naphthol and 1,1′-bi-2-phenol derivatives and chiral P-chirogenic compounds in optically active form. The reaction is applied for hydrolytic deallylation of N-allyl amide and allyl esters. The later one was achieved by palladium/ruthenium dual catalysts which is the first example of catalytic irreversible ester hydrolysis. Gold complexes also catalyzed vinyl ether alcoholysis and hydroalkoxylation of olefins. In the later reaction, simple unactivated olefins can be used as substrates and gave the product in 92% yield. The copper-DTBM-SEGPHOS complex catalyzed alcoholysis of azlactones which is the first example showing zero-order kinetic resolution.     

Highly enantioselective asymmetric hydrogenation of alpha-phthalimide ketone: an efficient entry to enantiomerically pure amino alcohols

A new type of alpha-phthalimide ketones was hydrogenated in excellent enantioselectivity by using a Ru-(C3-TunePhos) complex as the catalyst. Up to 10 000 turnovers have been achieved in more than 99% ee in the hydrogenation reaction. A dynamic kinetic resolution study for the synthesis of threonine was performed, and high anti selectivity (>97:3) was observed for the first time. An efficient method to synthesize enantiomerically pure amino alcohols has been developed.     

Highly selective palladium catalyzed kinetic resolution and enantioselective substitution of racemic allylic carbonates with sulfur nucleophiles: asymmetric synthesis of allylic sulfides,allylic sulfones,and allylic alcohols

We describe the highly selective palladium catalyzed kinetic resolutions of the racemic cyclic allylic carbonates rac-1 a-c and racemic acyclic allylic carbonates rac-3 aa and rac-3 ba through reaction with tert-butylsulfinate, tolylsulfinate, phenylsulfinate anions and 2-pyrimidinethiol by using N,N'-(1R,2R)-1,2-cyclohexanediylbis[2-(diphenylphosphino)-benzamide] (BPA) as ligand. Selectivities are expressed in yields and ee values of recovered substrate and product and in selectivity factors S. The reaction of the cyclohexenyl carbonate 1 a (>/=99 % ee) with 2-pyrimidinethiol in the presence of BPA was shown to exhibit, under the conditions used, an overall pseudo-zero order kinetics in regard to the allylic substrate. Also described are the highly selective palladium catalyzed asymmetric syntheses of the cyclic and acyclic allylic tert-butylsulfones 2 aa, 2 b, 2 c, 2 d and 4 a-c, respectively, and of the cyclic and acyclic allylic 2-pyrimidyl-, 2-pyridyl-, and 4-chlorophenylsulfides 5 aa, 5 b, 5 ab, 6 aa-ac, 6 ba and 6 bb, respectively, from the corresponding racemic carbonates and sulfinate anions and thiols, respectively, in the presence of BPA. Synthesis of the E-configured allylic sulfides 6 aa, 6 ab, 6 ac and 6 bb was accompanied by the formation of minor amounts of the corresponding Z isomers. The analogous synthesis of allylic tert-butylsulfides from allylic carbonates and tert-butylthiol by using BPA could not be achieved. Reaction of the cyclopentenyl esters rac-1 da and rac-1 db with 2-pyrimidinethiol gave the allylic sulfide 5 c having only a low ee value. Similar results were obtained in the case of the reaction of the cyclohexenyl carbonate rac-1 a and of the acyclic carbonates rac-3 aa and rac-3 ba with 2-pyridinethiol and lead to the formation of the sulfides 5 ab, 6 ab, and 6 bb, respectively. The low ee values may be ascribed to the operating of a "memory effect", that is, both enantiomers of the substrate give the substitution product with different enantioselectivities. However, in the reaction of the racemic carbonate rac-1 a as well as of the highly enriched enantiomers 1 a (>/=99 % ee) and ent-1 a (>/=99 % ee) with 2-pyrimidinethiol the ee values of the substrates and the substitution product remained constant until complete conversion. Similar results were obtained in the reaction of the cyclic carbonates rac-1 a, ent-1 a (>/=99 % ee) and ent-1 c (>/=99 % ee) with lithium tert-butylsulfinate. Thus, in the case of rac-1 a and 2-pyrimidinthiol and tert-butylsulfinate anion as nucleophiles the enantioselectivity of the substitution step is, under the conditions used, independent of the chirality of the substrate; this shows that no "memory effect" is operating in this case. Hydrolysis of the carbonates ent-1 a-c, ent-3 aa and ent-3 ba, which were obtained through kinetic resolution, afforded the enantiomerically highly enriched cyclic allylic alcohols 9 a-c (>/=99 % ee) and acyclic allylic alcohols 10 a (>/=99 % ee) and 10 b (99 % ee), respectively.