DMSO activators acetic anhydride

The initiating step in these reactions is the attachment of a group to the sulfoxide oxygen to produce an activated intermediate (5). Suitable groups are proton, acyl, alkyl, or almost any of the groups that also initiate the oxidations of alcohols with DMSO (40,48). In a reaction, eg, the one between DMSO and acetic anhydride, the second step is removal of a proton from an a-carbon to give an yUde (6). Release of an acetate ion generates the sulfur-stabilized carbonium ion (7), and the addition of acetate ion to the carbonium ion (7) results in the product (eq. 15) ... 

The one-step reaction of H2prCl6] with MeC02Li under 02 in a mixed solvent of acetic acid and acetic anhydride yields the Ir11 binuclear complex [Ir2(/u-02CMe)2Cl2(C0)2].483 Crystal-structure determinations of [Ir2(/x-02CMe)2Cl2(C0)2L2], (295), where L = MeCN, DMSO, and py, are reported. The one-electron oxidation product for (295), L = py, is EPR active at 77 K the odd electron occupies the 6Ir Ir orbital. 

There are several methods reported in the literature for transforming vicinal diols into ct-diketones while avoiding the risk of C-C bond cleavage.26 Examples include the standard Swem conditions (dimethyl sulfoxide and oxalyl chloride followed by triethylamine), or the use of DMSO activated by acetic anhydride, pyridine-sulfur trioxide complex, or dicyclohexylcarbodiimide (Mq/J-att oxidation). Diones are also obtained by treatment with benzalacetone as a hydride acceptor in the presence of catalytic amounts of tris(triphenylphosphine)ruthenium dichlonde [(PPh RuCFl.27 Recent developments include the use of w-iodoxyben/.oic acid28 or the oxoammonium salt of 4-acctamidoletramethylpipcridine-1-oxyl and y -toluencNulfonic acid.29... 

The desired oxidation of the alcohol was accompanied by a-chlorination of the cyclohexanone. The chlorination could be avoided by using a stoichiometric amount of activated DMSO, or by activating the DMSO with acetic anhydride. 

A variety of methods have been described to solve the task in solution.16 Common oxidative agents for this transformation include various heavy-metal reagents such as chromium-or ruthenium-based oxides, pyri-dine-S03, and dimethylsulfoxide (DMSO) in combination with acetic anhydride, carbodiimide, or oxalyl chloride for activation. One of the most prominent methods for the reliable conversion of sensitive compounds is the Dess-Martin reagent or its nonacetylated equivalent, 1-hydroxy-(17/)-benzo-l,2-iodoxol-3-one-l-oxide (2-iodoxybenzoic acid, IBX). 

In an example of the use of this activation method testosterone, with a IT -hydroxy group, was oxidized to A -androstene-3,17-dione very rapidly in high yield, in contrast to the use DMSO-acetic anhydride. During a reaction, when other oxidizing agents were found to be ineffective, sulfur trioxide/dimethyl sulfoxide led to smooth oxidation of the df-diol (16 equation 8) to an o-quinone in 49% yield and the ci.r-diol (17) to (18 equation 9) in 98% yield. - The use of dimethyl sulfoxide-acetic anhydride for this oxidation gave large amounts of the diacetate as the by-product. 

Protection of aldoses at the non-anomeric positions makes it possible to use many of the common procedures in organic chemistry for oxidizing lactols as shown with mannofura-nose 1 and glucopyranose 3 (O Table 1). The reactions can be divided into three main categories oxidations mediated by activated dimethyl sulfoxide (DMSO), oxidations with chromi-um(VI) oxides, and oxidations catalyzed by ruthenium oxides. The DMSO-mediated oxidations of alcohols can be promoted by several activators [27]. With the partially protected aldoses the activation has mainly been achieved with acetic anhydride and oxalyl chloride. Competing /3-elimination does usually not occur unless the eliminating group is an ester, e. g., an acetate or a benzoate [27]. 

Trifluoroacetic anhydride (TFAA) is also a very potent activator for DMSO and concomitant trifluoroacetylation of the starting alcohol is usually not observed [27]. Both the Swem and the TFAA procedure are carried out at low temperature to prevent undesired side reactions, particularly formation of the methylthiomethyl ether. Before these two methods became developed, acetic anhydride was often used for DMSO activation. Flowever, the oxidation under these conditions is slower and the methylthiomethyl ether byproduct is often observed [27]. 

C.iii. Other DMSO Oxidations. Albright and Goldman developed a reagent using DMSO and acetic anhydride that formed an active sulfoxonium complex. 12 jj (jje initial work, yohimbine was oxidized to the ketone (yohimbinone) in 85% yield, at ambient temperatures in 24 h. 2 As with DCC, DMSO initially reacts with acetic anhydride to form sulfoxonium salt 66, which then reacts with the alcohol. Acetate is the leaving... 

The starting material, l,3-dibenzyloxy-2-propanol 265, is easily oxidized to the ketone 408 using N-chlorosuccinimide and dimethyl sulfide. Compound 408 was smoothly converted into the epoxide 409. The epoxide ring was opened by the attack of benzylate anion at the least hindered site to produce 2-benzyloxymethyl-l,3-dibenzyloxy-2-propanol (410), which was activated as the thiomethyl ether system 411 using acetic anhydride in DMSO. The thiomethyl ether is readily activated by iodine, allowing nucleophilic attack at the methylene position. As a result, compound 411 was... 

Other reagents that have been found capable of activating DMSO toward nucleophilic attack include acetic anhydride and phosphorus pentoxide. ... 

DMSO/TBAF is highly efficient as a reaction medium for the homogeneous esterification of cellulose by transesterification and after the in situ activation (see below) of complex carboxylic acids. The acylation using acid chlorides and anhydrides is limited because the solution contains a certain amount of water caused by the use of the commercially available TBAF trihydrate and the residual moisture in the air-dried polysaccharides. Nevertheless, this system has shown a remarkable capacity for the esterification of lignocellulosic mataials, for example, sisal fibres, which contain about 14 per cent hemicellulose [28]. The DS values of cellulose acetate prepared from these fibres with acetic anhydride in mixtures of DMSO/TBAF were found to decrease with increasing TBAF concentration from 6 to 11 per cent (Table 16.4), due to the increased rate of hydrolysis both of the anhydride and the ester moieties. 

The system incorporates nine solvent/reagent reservoirs to enable delivery of the NMP main wash, neat piperidine deblock (diluted with main wash on line), 0.45 M HBTU-HOBt-DMF activator solution, 2.0 M DIPEA-NMP, MeOH final wash, DCM wash, alternative activators (e.g. 1.0 M DCC-NMP), capping solution, and solvent exchange for Fmoc/rBu chemistry. In the case of Boc/Bzl-based methods, DCM and NMP are used as the main wash solvents, TFA (diluted with DCM on-line) for deblock, 1.0 M DCC-NMP and 1.0 M HOBt-NMP for activation, DMSO-NMP (4 1) for improved solvation, acetic anhydride for capping, and MeOH for final wash. A gas positive-pressure chemical delivery system controls the flow of all reagents and solvents. Gas pressure is provided by an external tank of nitrogen. 

The solvent effect in Mn2(CO)io polymerizations was explored with over 40 solvents [51] and perfluorobutyl iodide (PFBI), easily activated by Mn(CO)5 (vide infra) was used as initiator. The comparisons were made under the same conditions (VDF/PFBI/Mn2(CO)io = 25/1/0.2 VDF/solvent = 1/3 wt/v) and revealed that in accordance with the principles outlined above, no polymerization occurred in anisole, a,a,a-trifluorotoluene, diglyme, diethylene glycol monoethyl ether, ethyl ether, THF, dioxane, o-cresol, isopropanol, trifluoroacetic anhydride, tetramethylurea, sulfolane, benzonitrile, cyclopentanone even after 1-3 days. Poor reaction rates (/ p PP < 1 - 9 X 10 h ) were observed in HMPA, 2-butanone, methyl pentanone, DMF, DMSO, PEO, DMAc, 5-valerolactone, BuOH, and EtOAc. Slightly faster polymerizations (/ p PP = 1 - 1.7 X 10 h ) were seen in CH2CI2, acetic anhydride, y-butyrolactone, 1,2-dichloroethane, TMP, MeOH, pentafluorobutane, and HFBz,... 

Fused Heteroaromatic Compounds.— The halogen in 4-chloroquinoline is readily replaced by the enolate anions from isopropylidine alkylmalonates and acetic anhydride in the presence of the heterocycle acylation of the nitrogen provides the necessary activation of the system. Attempted overall methylation of 2-methylquinoline by MeSOCH2 and DMSO gives only a minute amount of the... 

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