Aminoketones cyclic

A number of other simple cyclic amine targets with oxygen substitution have been prepared using a nitrone cycloaddition strategy to provide both the N- and 0-functionalities. These include the pyrrolidines darlinine 193 and analogues (248), (+)-preussin (194) (249) and the piperidines (—)-allosedamine (195) (250), and the related structure 196 (251) as well as analogous (3-aminoketones (Fig. 1.4) (252). 

Many other examples are known of acid-catalyzed intermolecular Schiff reactions18 to give cyclic dimers. Thus, condensation of two molecules of a-aminoketones gives 2,5-dihydropyrazines (e.g., 9 from l-aminopropan-2-one), most of which can be converted into pyrazines by oxidation with mercuric chloride (i.e., the Gutknecht pyrazine synthesis19). The same type of self-condensation occurs on heating... 

Other hydrogenolytic reactions, involving the R—CH2 bond between the substrate and the methylene group of the Mannich base, are carried out on the Mannich bases of succinimide, - on some thiazolidinc derivatives- - and on cyclic P-aminoketones. ... 

Pharmaceuticals made from Mannich bases are reported in Table 43, where almost the whole range of the different classes is represented. C-Mannich bases, in particular cyclic and acyclic P-aminoketones, predominate, although N-Mannich bases, especially amide derivatives, are also well represented. 

Removal of the amine moiety in piperazine derivatives in acidic medium " is thought to occur from the enolic form of the ammonium salt, at least at very low pH values. However,. step b has not been interpreted entirely from the mechanistic point of view, as far as the participation of ammonium/enolate structures is concerned. Several cyclic transition states have been envisaged, some of which involve the presence of a hydroxy group or the enolic form of the P-aminoketone. In particular, the participation of OH groups belonging to other molecules, such as carboxyacids present in the reaction medium, cannot be excluded. " By contrast, a nucleophilic attack by an acid anion on the carbonyl C atom has been claimed to be the rate-determining step for deamination in the reaction between p-aminoketones and triethyl phosphite in dimethylformamide. ... 

Opposite stereochemical results with re.spect to hydrogenation are obtained with cyclic (3-aminoketones of type 299, which include the Mannich bases of cyclohexanone (X =... 

Imidazolines can exist as three possible structures 2-imidazolines (171), 3-imidazolines (172) or 4-imidazolines (173) (Scheme 83). The first-named can exist as a pair of tautomers, but any proton shift in (172) will give (173) by rearrangement. In fact the hydrolysis of Af-unsubstituted 3-imidazolines to a-aminoketones occurs presumably via the 4-imidazoline. 2-Imidazolines are cyclic amidines, and as such exhibit the characteristic resonance stabilization and strongly basic natures of these compounds. Protonation occurs on the unsubstituted nitrogen to give a resonance-stabilized imidazolinium ion. Examples of p/fa... 

In situ formation of a-aminoketones has been achieved from the reaction of a-hydroxy- or a-haloketones with amines. l,3-Dihydroxypropan-2-one has been used as a starting material in the Marckwald synthesis <1997JME3297>. Also, reaction of 4-chloro-Wmethyl-3-oxobutanamide 1274 with amines leads to cyclic (E)-N-methyl-5-(methylimino)-2,5-dihydrofuran-3-amines 1275, which behave as latent a-aminoketones. Treatment of 1275 with isothiocyanates in refluxing EtOH affords imidazole-2-thiones 1276 (Scheme 323) <2005JC0826>. 

The reaction was applied successfully to cyclic vinyl azides to produce fused azirine rings. 1-Azido-cyclooctene (46) was converted on irradiation in 93% yield into 9-azabicyclo-[6.1.0]-non-l-(9)-ene (47). The azirine could again be hydrolysed to the aminoketone (48)... 

Amidines, cyclic Triethyl orthoformate. o-Aminoketones Sodium methoxide. 

The 1,3-dipolar cycloaddition follows with the regiochemistry shown 146a and the product is a bicyclic compound 147 with an N-0 single bond that is easily reduced to give a seven-membered cyclic aminoketone 148 with stereochemistry. 

The nitrosation method is not recommended for a-aminoketones, but it works well for 2-amino-l,3-dicarbonyl compounds, as found by Wolff (1902) for the preparation of 3-diazopentane-2,4-dione (2.31). Cyclic diazo-a, a -diketones, such as 2-diazocyclohexane-l,3-dione (2.32, R=H) and its 5,5-dimethyl derivative (diazo-dimedone, 2.32 R=CH3), can be synthesized without major difficulties (Eistert et al., 1959 Stetter and Kiehs, 1965). The parent compound, diazomalonodialdehyde (2.33) was prepared only in 1973 by Arnold and Sanliova. The smooth formation of diazo-a,a -diketones and the decreased tendency for proton addition at the central C-atom can be explained by the resonance structures 2.31 a-c. 

Vicario showed that a-aminoketones can function as nucleophiles towards unsaturated aldehydes. The initially formed product spontaneously cyclised to a cyclic aminal, which was then oxidised to chiral lactam. Cyclisation of the initial Michael addition product was also achieved using 8-hydroiyl enals. 2 ... 

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