Manganese dioxide methyl ester

Several total syntheses of antirhine (11) and 18,19-dihydroantirhine (14) have been developed during the last decade. Wenkert et al. (136) employed a facile route to ( )-18,19-dihydroantirhine, using lactone 196 as a key building block. Base-catalyzed condensation of methyl 4-methylnicotinate (193) with methyl oxalate, followed by hydrolysis, oxidative decarboxylation with alkaline hydrogen peroxide, and final esterification, resulted in methyl 4-(methoxycar-bonylmethyl)nicotinate (194). Condensation of 194 with acetaldehyde and subsequent reduction afforded nicotinic ester derivative 195, which was reduced with lithium aluminum hydride, and the diol product obtained was oxidized with manganese dioxide to yield the desired lactone 196. Alkylation of 196 with tryptophyl bromide (197) resulted in a pyridinium salt whose catalytic reduction... 

Oxidation of 48 using manganese dioxide in methanol in the presence of potassium cyanide provides clausine H (clauszoline-C) (50) quantitatively, which on ester cleavage affords clausine K (clauszoline-J) (51). Cleavage of both methyl ethers of 51 on treatment with boron tribromide led to clausine O (72) (588). 

The distribution of by-products originating from the methyl group in acetaldehyde oxidation is significantly different for each catalyst. Typical results are presented in Table II. Methane is the predominant by-product with cobalt acetate, while methane and carbon dioxide and methyl esters and carbon dioxide predominate with manganese and copper acetates, respectively. 

The structure of the methyl ester m.p. 174° C. (XL) was proven (5) mainly by the fact that the corresponding dibasic acid (XLI R = H) and its dimethyl ester (XLI R = Me) are oxidized with periodate and that the dimethyl ester is oxidized by manganese dioxide to a trisubstituted a,/ -unsaturated ketone (XLII) which regenerates (XLII R = Me) with sodium borohydride. 

The condensation, using heterogeneous catalysts, of methyl esters of acetic or propionic acids with formaldehyde to form methyl acrylate or methyl methacrylate has been the subject of a number of recent patents. Thus, lead acetate on silica 145), manganese dioxide on silica (146), and Ba-, Ca-, Sr-, and Mg- Decalso derivatives (147) have been effective catalysts for this reaction. 

Oxidative aromatization. Activated manganese dioxide (excess) oxidatively dehydrogenates certain cyclohexene aldehydes, ketones, and Schiff bases, but not esters, to the corresponding aromatic derivative. For example, 2-methyl-cyclohexene-3-carboxaldehyde (3 and 4), obtained by the Diels-Alder reaction of pentadiene-1,3(1) with acrolein (2) is oxidized to o-tolualdehyde (5) in 69% yield. 4-Acetylcyclohexene is oxidized to acetophenone in 71 % yield.3... 

Activated manganese dioxide is a closely related oxidant to Ni02 but less commonly used. Meguro, Fujita, and co-workers described oxidation of oxazolines using Mn02 in their synthesis of antidiabetic agents. For example, the serine-derived P-hydroxyamide 21 was cyclized to the oxazoline 22 with polyphosphoric acid. Oxidation of 22 with activated manganese dioxide afforded 2-styryl-4-oxazolecarboxylic acid methyl ester, 23 (Scheme 1.4). 

The seeds of Ipomoea violacea, variety Pearly gates , were earlier reported to contain an ergoline acid of unknown constitution, which proves to be chano-clavine-I acid (56), since reduction (LiAlH4) gives rise to chanoclavine-I (57) conversely, oxidation of chanoclavine-I by means of manganese dioxide gives the related aldehyde, which, on further oxidation by manganese dioxide in methanol in the presence of cyanide ion, affords chanoclavine-I acid methyl ester directly. " ... 

Compound 136 can be transformed to the 3,4-trans isomer 138, which has the same configuration as ( + ) thienamycin, according to the procedure described by Chiba and coworkers in related structures [74]. The method involved oxidation of the hydroxyl group in 136 with activated manganese dioxide with concomitant isomerization at C-3, followed by K-selectride reduction of the resulting methyl ketone 137. Zinc enolates of iV,iV-disubstituted a-aminoacid esters have also been recently utilized for the synthesis of 3-amino P-lactams [75]. 

It should be pointed out that manganese dioxide is a mild oxidant that usually converts primary allylic alcohols into conjugated aldehydes without significant further oxidation to carboxylic acids." However, in the presence of HCN and cyanide, the a, -unsaturated aldehydes could be converted into cyanohydrins, which are susceptible to the oxidation of Mn02 to acyl cyanides. In the presence of an alcohol, the a,j8-unsaturated esters are obtained. It should be emphasized that this reaction works only for a,j8-unsaturated aldehydes and will not cause any cis-trans isomerization for the a,/3-unsaturated double bond. For example, benzaldehyde (> 95%), cinnamaldehyde (> 95%), furfural (> 95%), geranial (85-95%), and farnesal (> 95%) have all been transformed into the corresponding methyl esters. ... 

A direct method for conversion of aldehydes to esters has been reported. It is applicable to a,j8-unsaturated aldehydes and aromatic aldehydes. The process involves stirring the aldehyde for several hours with sodium cyanide and manganese dioxide in a solution of methanol containing some acetic acid. The product is the methyl ester of the a,j8-unsaturated or aromatic carboxylic add. Indicate the basis for the success of this procedure. 

Thiosemicarbazones of 3-, 4-, and 5-methylisoquinoline-1-carboxaldehyde have also been synthesized [18] to assist in a definition of molecular dimensions compatible with biological activity. The syntheses of the methyl-substituted derivatives were accomplished by rearrangement of the N-oxides of 1,3-, and 1,4-dimethylisoquinoline with acetic anhydride followed by acid hydrolysis of the ester and subsequent oxidation of the carbinol with manganese dioxide. However, 1,5-dimethylisoquinoline (77) was selectively oxidized with selenium dioxide to the corresponding 1 [Pg.337]

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