Chemoselective Preparation of Oximes, Semicarbazones, and Tosylhydrazoneswithout Catalyst and Solvent

Summary.  A simple and versatile method for the synthesis of oximes, semicarbazones, and tosylhydrazones of aldehydes in the presence of ketones without catalyst and solvent is presented. Received June 28, 2000. Accepted (revised) August 25, 2000     

Basic Alumina as an Efficient Catalyst for Preparation of Semicarbazones in Solvent Free Conditions

An efficient and simple procedure for conversion of different classes of aldehydes and ketones into the corresponding semicarbazones with semicarbazide hydrochloride using basic alumina is studied.     

Carbonyl Regeneration from Oximes and Semicarbazones by Trimethylchlorosilane-Dimethylsulphoxide

Treatment of oximes and semicarbazones of saturated and α,β-unsaturated ketones and aldehydes with trimethylchlorosilane-dimethyl sulphoxide in dry acetonitrile affords the corresponding carbonyl compounds in excellent yields under mild conditions.     

Microwave Assisted Conversion of Oximes and Semicarbazones to Carbonyl Compounds Using Benzyltriphenylphosphonium Peroxymonosulfate

Summary.  Benzyltriphenylphosphonium peroxymonosulfate in the presence of catalytic amounts of bismuth chloride was found to be an efficient and mild reagent for the oxidative cleavage of oximes and semicarbazones to the corresponding carbonyl compounds under microwave irradiation. Corresponding author. E-mail: haji@cc.iut.ac.ir Received March 4, 2002; accepted (revised) April 8, 2002     

Highly Selective Regeneration of Carbonyl Compounds from Their Oximes and Semicarbazones in Aqueous Medium

Abstract

Chemoselective regeneration of aryl alkyl ketone, α‐tetralone, and cycloalkanone by hydrolysis of their oximes and semicarbazones has been accomplished using aqueous phosphoric acid without involvement of any organic cosolvent in the reaction medium, where the similar derivatives of aryl aldehyde, diaryl ketone, aliphatic acyclic aldehyde and ketone remain mostly inert.     

Silica Chloride/Wet SiO2 as a Novel Heterogeneous System for Deprotection of Oximes,Hydrazones, and Semicarbazones

Abstract

Oximes, hydrazones, and semicarbazones can be converted to their corresponding carbonyl compounds in good to high yields by a combination of silica chloride and wet SiO₂.     

An Efficient,Selective and Inexpensive Supported Oxidant for the Regeneration of Carbonyl Compounds from Oximes,Semicarbazones, 4-Phenylsemicarbazones,and P-Nitrophenylhydrazones

Dimethylammonium chlorochromate adsorbed on silica gel (DMCC/SiO₂) makes the regeneration of carbonyl compounds from oximes, semicarbazones, 4-phenyl-semicarbazones, and p-nitrophenylhydrazones in good yields under mild and non-aqueous conditions.     

Deprotection of Oximes,Phenylhydrazones, Semicarbazones and Thiosemicarbazones to the Corresponding Carbonyl Compounds Using Cetyltrimethylammonium Peroxodisulfate as a New and Selective Oxidizing Agent

Cetyltrimethylammonium peroxodisulfate (CTA)₂S₂O₈ was quantitatively prepared and used for the deprotection of oximes, phenylhydrazones, semicarbazones and thiosemicarbazones to the corresponding carbonyl compounds in acetonitrile. Its agent is more efficient and has advantages over similar reagents in terms of the amount of oxidant, short reaction time, simple work up, and high yield.     

Development of a Practical and Scalable Preparation using Sonication of Pd/Fibroin Catalyst for Chemoselective Hydrogenation

A practical and efficient preparation method of palladium‐fibroin (Pd/Fib), silk‐fibroin‐supported Pd(0) by means of sonication, has been developed. The Pd/Fib catalyst could be prepared within 12 h at room temperature starting from commercial silk‐fibroin and Pd(OAc)₂ in MeOH, whereas our previous preparation method required at least 4 days. The present improved process is applicable to a large‐scale preparation of Pd/Fib. The Pd/Fib prepared by the present method also catalyzed chemoselective hydrogenation of acetylenes, olefins, and azides in the presence of aromatic ketones, aldehydes, and halides; N‐Cbz protective groups; and benzyl esters, which are readily hydrogenated under the Pd/C‐ or Pd/C(en)‐catalyzed hydrogenation conditions.     

Chemoselective Oxidation of Alkenes by Metal-Organic Framework-Supported Copper Catalyst

Oxidation of alkenes to carbonyls or diols compounds is important in synthesizing fine chemicals and pharmaceutical intermediates. We report the synthesis and characterization of an aluminum metal-organic framework node-supported copper(II) chloride (DUT-5-CuCl), which is an efficient heterogeneous catalyst for the oxidation of alkenes using H₂O₂ as an oxidizing agent. Styrene and various substituted styrenes were transformed into the corresponding carbonyl compounds in excellent selectivity and yields. DUT-5-CuCl is tolerant with various functional groups and could be recycled and reused at least 5 times in the oxidation of α-methylstyrene. Unlike the oxidation of styrene derivatives, DUT-5-Cu catalyzed oxidation of aliphatic and cyclic alkenes produced 1,2-diols compounds selectively. The mechanism of the DUT-5-Cu catalyzed oxidation of styrene to benzaldehyde was investigated in detail by various experiments such as the determination of reaction intermediates and characterization of the catalyst after catalysis, and computational studies. This work highlights the importance of MOF-supported earth-abundant metal catalysts for oxidation reactions to produce fine chemicals.     

Amberlyst-15 as a Convenient Catalyst for Chemoselective Thioacetalization

A new, mild and chemoselective protection of aldehydes as 1,3-dithiolanes is described. High yields are obtained at room temperature even in the presence of ketones. Ketones may also be protected at elevated temperatures.     

Chemoselective Electrochemical Hydrogenation of Ketones and Aldehydes with a Well-Defined Base-Metal Catalyst

Hydrogenation reactions are fundamental functional group transformations in chemical synthesis. Here, we introduce an electrochemical method for the hydrogenation of ketones and aldehydes by in situ formation of a Mn-H species. We utilise protons and electric current as surrogate for H₂ and a base-metal complex to form selectively the alcohols. The method is chemoselective for the hydrogenation of C=O bonds over C=C bonds. Mechanistic studies revealed initial 3 e⁻ reduction of the catalyst forming the steady state species [Mn₂(H₋₁L)(CO)₆]⁻. Subsequently, we assume protonation, reduction and internal proton shift forming the hydride species. Finally, the transfer of the hydride and a proton to the ketone yields the alcohol and the steady state species is regenerated via reduction. The interplay of two manganese centres and the internal proton relay represent the key features for ketone and aldehyde reduction as the respective mononuclear complex and the complex without the proton relay are barely active.     

Zinc Chloride as an Efficient Catalyst for Chemoselective Dimethyl Acetalization

Commercially available anhydrous zinc chloride has been found to be a highly efficient catalyst for dimethyl acetalization in high yields by treatment of aldehydes and ketones with trimethyl orthoformate in methanol-cyclohexane at reflux temperature.     

Alumina Sulfuric Acid as an Efficient and Recyclable Heterogeneous Catalyst for the O-Silylation of Alcohols,Phenols, and Oximes

Alumina sulfuric acid as a recyclable catalyst conducts the transformation of various types of alcohol, phenols, and oximes with hexamethyldisilazane (HMDS) to the corresponding O-trimethylsilylated compounds in good to excellent yields under mild and ambient conditions with short reaction times. The method is highly selective for the conversion of primary alcohols in the presence of secondary and tertiary alcohols. Additionally, the catalyst can be easily recovered and reused at least eight times without detectable loss of reactivity.     

Succinimide-N-Sulfonic Acid: A Mild,Efficient, and Reusable Catalyst for the Chemoselective Trimethylsilylation of Alcohols and Phenols

Abstract

Succinimide-N-sulfonic acid (SuSA) is easily prepared by the reaction of succinimide with chlorosulfonic acid. This reagent is able to efficiently catalyze the chemoselective trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS). All reactions were performed under mild reaction conditions, giving excellent yields.

GRAPHICAL ABSTRACT      

Chemoselective Dithioacetalization and Oxathioacetalization of Carbonyl Compounds Using Alumina Sulfuric Acid as Catalyst

Carbonyl compounds have been successfully converted into their corresponding dithiolane, dithiane, and oxathiolane derivatives using a catalytic amount of alumina sulfuric acid (Al₂O₃–SO₃H) with excellent yields at room temperature in short reaction times under mild conditions. This simple method is a highly chemoselective procedure for protection of aldehydes in the presence of ketones, and the heterogeneous catalyst can be recovered and reused several times without any loss of its activity.     

Preparation and Characterization of Some Novel Diphenylphosphine Hydrazones and Semicarbazones and Their Metal Complex Derivatives

Interaction of hydrazones and semicarbazones derivatives I _{a ? t} with diphenylchlorophosphine II , gave new compounds III _a?t , and their complexation ability towards various divalent metal acetates Mn(OAc)₂. 4H₂O, Co(OAc)₂. 4H₂O, Ni(OAc)₂. 4H₂O, and Cu(OAc)₂. H₂O, in organic solvents are described. The metal/ phosphorsemi-carbazones ratios are measured and the results discussed. All these complexes are insoluble in organic solvents and in water. The structures of the isolated products were proposed on the basis of microanalyical data, TGA, IR, (UV/ VIS), (MS), and ¹H, ¹³C, and ³¹P-NMR spectroscopic analyses and magnetic susceptibility. The proposed structure of the complexes is based on a 1: 2 metal: ligand ratio. All of the complexes are found to have an octahedral geometry, with the exception of the square planar copper (II) complexes. The corrosion inhibition of aluminium and copper in 1 M HCl and chromium–nickel steel in crude oil using III_n have been studied by weight loss method.     

Highly Chemoselective Catalytic Photooxidations by Using Solvent as a Sacrificial Electron Acceptor

Catalyst recovery is an integral part of photoredox catalysis. It is often solved by adding another component-a sacrificial agent-whose role is to convert the catalyst back into its original oxidation state. However, an additive may cause a side reaction thus decreasing the selectivity and overall efficiency. Herein, we present a novel approach towards chemoselective photooxidation reactions based on suitable solvent-acetonitrile acting simultaneously as an electron acceptor for catalyst recovery, and on anaerobic conditions. This is allowed by the unique properties of the catalyst, 7,8-dimethoxy-3-methyl-5-phenyl-5-deazaflavinium chloride existing in both strongly oxidizing and reducing forms, whose strength is increased by excitation with visible light. Usefulness of this system is demonstrated in chemoselective dehydrogenations of 4-methoxy- and 4-chlorobenzyl alcohols to aldehydes without over-oxidation to benzoic acids achieving yields up to 70 %. 4-Substituted 1-phenylethanols were oxidized to ketones with yields 80–100 % and, moreover, with yields 31-98 % in the presence of benzylic methyl group, diphenylmethane or thioanisole which are readily oxidized in the presence of oxygen but these were untouched with our system. Mechanistic studies based on UV-Vis spectro-electrochemistry, EPR and time-resolved spectroscopy measurements showed that the process involving an electron release from an excited deazaflavin radical to acetonitrile under formation of solvated electron is crucial for the catalyst recovery.