烯丙醇化合物的不对称环氧化

本文报道了三个脂肪族烯丙醇化合物(1-3)的不对称环氧化反应。由反式烯丙醇2得到的反式烯丙醇环氧化合物2a的对映体过量大于由顺式烯丙醇1得到的环氧化合物1a的对映体过量。叔羟基二取代烯丙醇3经不对称环氧化生成的3a,其对映体过量只有4%。     

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%).     

Kinetic Resolution of Tertiary 2‐Alkoxycarboxamido‐Substituted Allylic Alcohols by Chiral Phosphoric Acid Catalyzed Intramolecular Transesterification

A highly enantioselective kinetic resolution of tertiary 2‐alkoxycarboxamido allylic alcohols has been achieved through a chiral phosphoric acid catalyzed intramolecular transesterification reaction. Both alkyl,aryl‐ and dialkyl‐substituted tertiary allylic alcohols were resolved with excellent efficiencies, affording both the recovered tertiary alcohols and the carbamate products with high enantioselectivities (with s factors up to 164.6). A gram‐scale reaction with 1 mol % catalyst loading and the facile conversion of the enantioenriched products into useful chiral building blocks, such as chiral oxazolidinones and β‐amino alcohols, demonstrate the value of this reaction.     

Transition‐Metal‐Free Borylation of Allylic and Propargylic Alcohols

The base‐catalyzed allylic borylation of tertiary allylic alcohols allows the synthesis of 1,1‐disubstituted allyl boronates, in moderate to high yield. The unexpected tandem performance of the Lewis acid–base adduct, [Hbase]⁺[MeO‐B₂pin₂]^? favored the formation of 1,2,3‐triborylated species from the tertiary allylic alcohols and 1‐propargylic cyclohexanol at 90 °C.     

在氢化钙-硅胶存在下的烯丙醇催化不对称环氧化

自从 Sharpless 不对称环氧化被发现以来,这个反应已被广泛地应用于手性天然产物的合成。最近,Sharpless 及其同工作者又将原方法中使用的等摩尔量四异丙氧基钛和酒石酸酯减少到催化量,并加入3(?)或4(?)分子筛。这一改进可减少敏感性环氧醇产物的破环,使产物易于分离。从而使这个方法变得更为经济简便。我们曾报道过的改良 Sharpless     

Liquid-phase synthesis of chiral tartrate ligand library for enantioselective sharpless epoxidation of allylic alcohols

This paper reports a successful development of a group of efficient soluble polymer-supported chiral tartrate ligands by liquid-phase synthesis for Sharpless epoxidation of a variety of allylic alcohols through ligand diversity. The influence of substituent in chiral tartrate ligands on the enantioselectivities of the reaction was disclosed. Moderate chemical yields and good enantiomeric excesses were obtained by using soluble polymer-supported tartrate ester in the epoxidation of allylic alcohols with Ti(O-i-Pr)(4)/tert-butyl hydroperoxide.     

Asymmetric addition of alkylzinc reagents to cyclic alpha,beta-unsaturated ketones and a tandem enantioselective addition/diastereoselective epoxidation with dioxygen

Although over 100 catalysts have been reported to catalyze the asymmetric addition of alkyl groups to aldehydes, these catalysts fail to promote additions to ketones with >90% enantioselectivity. This paper describes the asymmetric 1,2-addition of alkyl groups to conjugated cyclic enones to give allylic alcohols with chiral quaternary centers. The resultant allylic alcohols are converted into epoxy alcohols with excellent diastereoselectivities. Treatment of the epoxy alcohols with BF3.OEt2 induces a semipinacol rearrangement to provide alpha,alpha-dialkyl-beta-hydroxy ketones with all-carbon chiral quaternary centers. We also report a one-pot procedure for the asymmetric addition/diastereoselective epoxidation reaction. Simply exposing the reaction mixture to dioxygen after the asymmetric addition reaction is complete results in epoxidation of the allylic alcohol with high diastereoselectivity.     

Oxidation of alcohols with oxoperoxobis(N-phenylbenzohydroxamato)molybdenum(VI)

The title complex oxidizes primary and secondary alcohols to the corresponding carbonyl compounds. Stereoselective epoxidation of allylic alcohols is also described.     

Selective oxidation with t-butyl hydroperoxide and aluminium reagents

Stereoselective epoxidation of allylic alcohols is achieved with organoaluminium peroxides. Transformation of secondary alcohols to ketones with same reagents is also disclosed.     

Catalytic asymmetric allylation of ketones and a tandem asymmetric allylation/diastereoselective epoxidation of cyclic enones

A simple procedure is reported for the catalytic asymmetric allylation of ketones, utilizing titanium tetraisopropoxide, BINOL, 2-propanol additive, and tetraallylstannane as allylating agent. A variety of ketone substrates, including acetophenone derivatives and alpha,beta-unsaturated cyclic enones, reacted to form tertiary homoallylic alcohols in good yields (67-99%) and with high levels of enantioselectivity (generally >80%). A novel one-pot enantioselective allylation/diastereoselective epoxidation has also been introduced. Thus, upon completion of the allyl addition to conjugated cyclic enones, 1 equiv of tert-butyl hydroperoxide is added and the directed epoxidation of the allylic double bond ensues to afford the epoxy alcohol with high diastereoselectivity.     

Stereoselective expoxidation of allylic and homoallylic alcohols with 30% hydrogen peroxide catalyzed by tungstic acid in buffered media

The aqueous tungstic acid-catalyzed hydrogen peroxide epoxidation of allylic alcohols affords the same major diastereoisomer as the VO(acac)₂/tBuOOH system with quite comparable stereoselectivities. In contrast, epoxidation of homoallylic alcohols appears to be much less stereoselective.     

Asymmetric Cascade Reaction to Allylic Sulfonamides from Allylic Alcohols by Palladium(II)/Base‐Catalyzed Rearrangement of Allylic Carbamates

A regio‐ and enantioselective tandem reaction is reported capable of directly transforming readily accessible achiral allylic alcohols into chiral sulfonyl‐protected allylic amines. The reaction is catalyzed by the cooperative action of a chiral ferrocene palladacycle and a tertiary amine base and combines high step‐economy with operational simplicity (e.g. no need for inert‐gas atmosphere or catalyst activation). Mechanistic studies support a Pd^II‐catalyzed [3,3] rearrangement of allylic carbamates—generated in situ from the allylic alcohol and an isocyanate—as the key step, which is followed by a decarboxylation.     

Validity of Inorganic Nanosheets as an Efficient Planar Substituent To Enhance the Enantioselectivity of Transition‐Metal‐Catalyzed Asymmetric Synthesis

Effectively enhancing the enantioselectivity is a persistent challenge in heterogeneous asymmetric catalysis. Here, the validity of a layered double hydroxides (LDH) nanosheet as an efficient planar substituent to enhance the enantioselectivity has been investigated theoretically; first in vanadium‐catalyzed asymmetric epoxidation of allylic alcohols, and then in zinc‐catalyzed direct asymmetric aldol addition. The computational predication is further confirmed experimentally in zinc‐catalyzed direct asymmetric aldol addition by controlling the location of catalytic sites.     

Ligand-accelerated vanadium-catalysed epoxidation in water

Vanadium-catalysed epoxidation of allylic alcohols, a classical example of ligand-decelerated catalysis, in water it turns into a ligand-accelerated process.     

Highly enantio- and diastereoselective one-pot synthesis of acyclic epoxy alcohols with three contiguous stereocenters

Two highly enantio- and diastereoselective one-pot procedures for the synthesis of epoxy alcohols with up to three contiguous stereocenters are reported. Route one involves asymmetric addition of an alkylzinc reagent to an enal followed by diastereoselective epoxidation. Route two entails asymmetric vinylation of an aldehyde with divinylzinc reagents and subsequent diastereoselective epoxidation. The oxidant for the epoxidation is generated by exposure of the allylic alkoxide intermediate and the remaining organozinc reagent to dioxygen. Upon addition of catalytic titanium tetraisopropoxide, the directed epoxidation yields the epoxy alcohols with good to excellent yields.     

Facile Method for Trimethylsilylation of Alcohols using Hexamethyldisilazane and Ammonium Thiocyanate under Neutral Conditions

A highly efficient method for trimethylsilylation of primary, secondary, tertiary, allylic, and a variety of sugar‐derived alcohols using hexamethyldisilazane in the presence of a catalytic amount of ammonium thiocyanate under neutral conditions is reported.     

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.     

Asymmetric epoxidation of allylic alcohols employing 4,5-diphenyloxazole as a masked ester functionality

The 4,5-diphenyloxazolyl moiety has been found to be a masked ester functionality fully compatible with the Sharpless epoxidation of allylic alcohols within the same molecule.     

The role of trimethylsilyl group in highly stereoselective eposidation of allylic alcohols

The epoxidation of allylic alcohols carrying Me₃Si group on the double bonds with VO(acac)2-tBuOOH or MCPBA provides erythro or threo epoxy alcohols, respectively with high stereoselectivity.     

A straightforward strategy for the efficient synthesis of acrylate and phosphine oxide‐containing vegetable oils and their crosslinked materials

Phosphorus‐containing triglycerides were prepared from a new route that involves the singlet oxygen photo‐oxygenation of high oleic sunflower oil and further reduction of the resulting hydroperoxide derivatives to a mixture of secondary allylic alcohols. These allylic alcohols in presence of chlorodiphenylphosphine give allylic phosphinites capable to undergo a [2,3]‐sigmatropic rearrangement leading to tertiary phosphine oxides directly linked to triglyceride in a one‐pot two‐step reaction. The obtained phosphorus‐containing triglycerides with different hydroxyl content were activated to polymerization by acrylation and these acrylate triglycerides were radically crosslinked in presence of different amounts of pentaerythritol tetra‐acrylate. The thermal, dynamic‐mechanical, and flame retardancy properties of the final materials were evaluated. Thermal and thermo‐oxidative degradation was studied by gas chromatography/mass spectrometry, ³¹P HR‐MAS NMR spectroscopy, and scanning electron microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4051–4063, 2009