Dehydrogenation manganese dioxide

Manganese dioxide on bentonite clay has also been used for oxidation of phenols to quinones (30-100%) [97] and Mn02 on silica effects the dehydrogenation of pyrrolidines (58-96%) [98]. 

Chemical manganese dioxide (CMD). This form of Mn02 is used for batteries it is available from I. C. Sample office (Cleveland, Ohio, 44101). Shioiri et al. report it is superior to commercial activated Mn02 (Aldrich) and more convenient than freshly prepared activated Mn02 for dehydrogenation of 2-(l-ami-noalkyl)thiazolidine-4-carboxylic acids to the corresponding thiazoles (thiazole amino acids). 

Other chemical reagents that have been used to dehydrogenate are diphenyl disulfide for 1,2,3,4-tetrahydrocarbazole itself, N-bromosuccinimide in pyridine for 1-ethoxycarbonyl-1,2,3,4-tetrahydrocarbazole, selenium dioxide for 9-methyl-1,2,3,4-tetrahydrocarbazole (a 1 5 mixture of 9-methyl-carbazole and 1-oxo-1,2,3,4-tetrahydrocarbazole was obtained ), and manganese dioxide to aromatize 1-methyl- and l,4-dimethyl-6-alkoxy-3-formyl-1,2,3,4-tetrahydrocarbazoles and 1,9-diprenyl-1,4-dihydrocarba-zole. ... 

Cycloaddition reactions of nitrile oxides continue to be the source of new isoxazoles and dihydroisoxazoles. The oxidation of a-hydroxyimino acids 1 by ammonium hexanitratocerium(IV) has provided a new method of generation of benzonitrile oxide and other nitrile oxides on the other hand the oxime 2 is simply dehydrogenated by this oxidant to produce benzoylnitrile oxide <99BSJ2277>. Manganese dioxide has also been used to oxidise aldoximes to nitrile oxides the reaction is most efficient with methyl (hydroxyimino)acetate <99TL5605>. ... 

Carbodiimides undergo a [4-1-2] cycloaddition reaction to form pyrrolo[3,4-f]pyridine derivatives <1998J(P1)3065>. Dehydrogenation of the cycloadduct in the presence of manganese dioxide gives improved yields (Scheme 8). 

Dehydrogenation of 1,2-dehydropyrroltzidines. Oxidation of retronecine (1) with Fremy s salt gives dehydroretronecine (2) in satisfactory yield.2 This oxidation has been conducted with chloranil, manganese dioxide, and potassium permanganate, but yields are lower.3... 

A general method of potential synthetic usefulness is the preparation of aromatic azapentalenes by oxidation of partially saturated systems. This has been used with success in a few cases (e.g., Sections III,A,3,d,108,109 III,B,3,c,293-295 III,A,284), but it has not been extensively explored. Recently, several workers have reported some possibly significant failures while attempting the dehydrogenation of nonaromatic systems. Various 2,3-dihydroimidazo[l,2-h]pyrazoles resisted oxidation to the corresponding aromatic system with manganese dioxide, chloranil, or dicyanodichloroquinone (DDQ),355 and a... 

N-Acylation, reduction of nitro to amino, and condensation produce dihydrotriazine 5.31. This system is readily dehydrogenated with manganese dioxide to afford the fully aromatic heterocycle 5.32. Note how relatively simple chemistry can be used to form a quite complex heterocycle. 

Very recently it has been reported that 4,5-dihydroisoxazoles are dehydrogenated essentially quantitatively by treatment with active y-manganese dioxide, the water formed in the reaction being removed by azeotropic distillation.114... 

Although the methods discussed in earlier sections generally constimte the preferred procedures by which to dehydrogenate carbonyl and similar compounds, a variety of other reagents will effect this transformation, and in some instances may offer certain advantages. Manganese dioxide is one reagent... 

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