István E. Markó

Copper-Catalyzed Oxidation of Alcohols to Aldehydes and Ketones: An Efficient, Aerobic Alternative

An efficient, copper-based catalyst has been discovered that oxidizes a wide range of alcohols into aldehydes and ketones under mild conditions. This catalytic system utilizes oxygen or air as the ultimate, stoichiometric oxidant, producing water as the only by-product.

Efficient, ecologically benign, aerobic oxidation of alcohols

Publisher Summary This chapter discusses aerobic oxidation of alcohols. The transformation of alcohols into aldehydes and ketones is of paramount importance in organic chemistry, both for laboratory-scale experiments and in the manufacturing processes. During the establishment of the scope and limitations of a useful catalytic process, some mechanistic studies are performed that allow proposing a plausible catalytic cycle, rationalizing our observations. It is remarkable that essentially every type of alcohol is smoothly oxidized into the corresponding carbonyl derivative in high yield and with good to complete conversion. Under these conditions, primary aliphatic, allylic, and benzylic alcohols afford the expected aldehydes, and secondary alcohols are smoothly transformed into ketones. Whereas, the decay of the alcohol follows the expected kinetic course, the formation of the aldehyde shows an abnormal behavior. In the early part of the reaction, the aldehyde formation matches almost perfectly the disappearance of the alcohol.

Catalytic enantioselective Baylis-Hillman reactions. Correlation between pressure and enantiomeric excess

Several chiral amino-alcohols induce asymmetry in the Baylis-Hillman condensation of aldehydes with methyl vinyl ketone. Pressure plays an interesting role in this reaction. A model accounting for the pressure effect and rationalising the observed absolute stereochemistry is discussed. Copyright (C) 1996 Elsevier Science Ltd

Highly beta-(E)-selective hydrosilylation of terminal and internal alkynes catalyzed by a (IPr)Pt(diene) complex.

The regioselective hydrosilylation of terminal and internal alkynes catalyzed by the novel (IPr)Pt(AE) ( 7) (IPr = bis(2,6-diisopropylphenyl)imidazo-2-ylidene, AE = allyl ether) complex is presented. The (IPr)Pt(AE) catalyst displays enhanced activity and regioselectivity for the hydrosilylation of terminal and internal alkynes with low catalyst loading (0.1 to 0.05 mol %) when compared to the parent (IPr)Pt(DVDS) complex ( 6) (DVDS = divinyltetramethyldisiloxane). The reaction leads to exquisite regioselectivity in favor of the cis-addition product on the less hindered terminus of terminal and internal alkynes. The solvent effects were examined for the difficult hydrosilylation of benzylpropargyl ether. In light of the observed product distribution and kinetic data, a mechanistic scheme is proposed involving two competing catalytic cycles. One cycle leads to high regioselectivities while the other, having lost the stereodirecting IPr carbene ligand, displays low regiocontrol and activities. The importance of this secondary catalytic cycle is either caused by the strong coordinating ability of the alkyne or by the low reactivity of the silane or both.

Cerium(IV)-Catalyzed Deprotection of Acetals and Ketals under Mildly Basic Conditions.

Smooth and quantitative deprotection of a wide range of acetals and ketals [Eq. (a); R, R(1)=alkyl, aryl, H] under neutral to mildly basic conditions was achieved with catalytic quantities of cerium ammonium nitrate (CAN). The reaction conditions are compatible with a variety of sensitive functional groups, and aldehydes can be liberated from acetals without being oxidized to the corresponding carboxylic acids.

The silyl modified sakurai (SMS) reaction. An efficient and versatile one-pot synthesis of homoallylic ethers

Abstract An efficient and versatile preparation of homoallylic ethers from trimethylsilyl ethers, allyltrimethylsilane and carbonyl compounds is described. Some preliminary experiments, aimed at controlling the diastereofacial selection in the SMS reaction, are also reported.

Stereoselective epoxidation of hydroxyenones. The synthesis of the sidechain of clerocidin

Abstract The sidechains of clerocidin 1 and terpentecin 2 contain a unique chiral assembly [C 5 H 5 O 4 ]. Models for the stereospecific synthesis of this structural feature are reported.

Radical mediated oxidations in organic chemistry. 3. An efficient and versatile transformation of aldehydes into amides

Abstract The neutral, radical-mediated, oxidation of aldehydes into acid bromides and amides is reported.

The Intramolecular Silyl-Modified Sakurai (ISMS) reaction. Synthetic studies towards ambruticine

The ISMS reaction has been used to efficiently construct the right-hand portion 3 of the antifungal antibiotic ambruticine 1.

Functionalized Orthoesters as Powerful Building Blocks for the Efficient Preparation of Heteroaromatic Bicycles

By combining substituted anilines with functionalized orthoesters, an efficient and connective methodology for the preparation of benzoxazole, benzothiazole, and benzimidazole derivatives has been established. The versatility of this approach enables the development of new libraries of heterocycles containing multifunctional sites.