Hydrogenation V Carbonyl Compounds

Baniwati, B., Polshettiwar, V., Varma, R. S. (2009). Magnetically recoverable supported ruthenium catalyst for hydrogenation of alkynes and transfer hydrogenation of carbonyl compounds. Tetrahedron Letters, 50, 1215—1218. http //dx.doi.org/10.1016/ j.tetiet.2009.01.014. 

The most widely employed methods for the synthesis of nitrones are the condensation of carbonyl compounds with A-hydroxylamines5 and the oxidation of A+V-di substituted hydroxylamines.5 9 Practical and reliable methods for the oxidation of more easily available secondary amines have become available only recently.10 11 12 13. These include reactions with stoichiometric oxidants not readily available, such as dimethyldioxirane10 or A-phenylsulfonyl-C-phenyloxaziridine,11 and oxidations with hydrogen peroxide catalyzed by Na2W044 12 or Se02.13 All these methods suffer from limitations in scope and substrate tolerance. For example, oxidations with dimethyldioxirane seem to be limited to arylmethanamines and the above mentioned catalytic oxidations have been reported (and we have experienced as well) to give... 

Up to about 10 percent of crs-stilbene was obtained when trimethyl-dioxetane 129 was decomposed in the presence of trans-stilbene 182) the electronic excitation energy of the excited carbonyl compounds formed in the cleavage of 129 (see Section V.) was transferred to trans-stilbene, so effecting the photochemical trans-cis isomerization. When bis (2.4-dinitrophenyl) oxalate reacted with hydrogen peroxide (see Section V. C. in the presence of o-tolyl-propane-1.2-dione 130, 2-methyl-2-... 

If, however, hydrogen is present in the a-position of the (V-alkyl substituent, 2-alkyl-oxaziridines are easily decomposed by alkali. Base attack on this H atom effects 1,2-elimination at the C—N bond. From (86) and aldimine (87) forms, and a mixture of ammonia and two carbonyl compounds is finally obtained, one of them containing the carbon atom of the original oxaziridine ring, the other originating from the N-alkyl group (57JA5739). 

The probable mechanism of the reaction is first addition of piperidine to formaldehyde to form /V-hydroxymethylpiperidine. This reacts with acidic hydrogens of the methyl group of 1,1,1-trifluoroacetone, which is hydrated because the trifluoromethyl group next to carbonyl stabilizes the hydrated form of the carbonyl compound. The resulting dihydrate is further stabilized by hydrogen bonds to the piperidine nitrogen 103. ... 

The iV-alkylation was considered to occur by the reaction of the carbonyl compounds, formed by the dehydrogenation of alcohols over the catalyst, with the hydrogenation products of pyridine,25 as suggested by Schwoegler and Adkins, who obtained good yields of /V-alkylpiperidines by the reaction of piperidine with alcohols.26 Maruoka et al. obtained a higher maximal yield of the iV-ethylated product in ethanol over Raney Co than over Raney Ni in the hydrogenation of 5-ethyl-2-methylpyridine (eq. 12.16),23 an alkylated pyridine prepared industrially by the reaction of acetaldehyde with ammonia. 

An acyclic v c-diimine was hydrogenated at a mercury cathode to give a mixture of the dj- and me o-diamines in 70% yield [183]. Imines can be stereoselectively hydrodi-merized to 1,2-diamines in a manner similar to the hydrodimerization of carbonyl compounds to pinacols [184,185]. 

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