Enamine chemistry—XVIII: The formation of hexahydrochromane-8a-amines by reductive cyclisation of enamines

Enamines (1) derived from cyclohexanone or cyclopentanone are reacted with electrophilic olefins (ethyl acrylate, ethyl 2-methylacrylate, ethyl 2-butenoate) to give the new enamines, 2. When 2 is reacted with LiAlH₄, reductive cyclisation takes place giving hexahydrochromane-8a-amines of octahydrocyclopentapyrane-7a-amines, 3, in quantitative yields. 3 is hydrolyzed with dilute aqueous hydrochloric acid to hexahydrochromane-8a-ols of octahydrocyclopentapyrane-7a-ols (4) and reacts also with oxalic acid in refluxing dioxane to form the condensed dihydropyranes, 5.     

Enamine Chemistry—XXIV.: Synthesis,thiation, and reduction of lactams

Enamines, 1, prepared from cyclohexanones or cyclopentanones are reacted with acrylamide to give lactams, the condensed 2-piperidones, 2. Ethyl 2-(1-pyrrolidinyl)-2-cyclohexene-1-propanoate, 3, when treated with primary amines, produces the corresponding N-substituted 2-piperidones, 4. Ethyl 2-(1-pyrrolidinyl)-2-cyclohexene-1-ethanoates and ethyl 2-(1-pyrrolidinyl)-2-cyclopentene-1-ethanoate, 5, react with primary amines to give condensed N-substituted 2-pyrrolidones, 6, and non-cyclic imines, 7. The starting enamines, 1, treated with 2-bromo acetamides only afford the N-alkylated compounds 8 (2-pyrrolidino acetamides), and the regioselectivity of this reaction is rationalized in terms of the HSAB-principle. Compound 1 undergoes an exchange reaction (aminolysis) when reacted with primary amines to give the imines 9. Thiation of the lactams 2 and 6 with the Lawesson reagent (LR), affords the corresponding thiolactams, 10. Reduction of the lactams and thiolactams, 2, 6, and 10 by LAH gives the imines, 11, and the enamines, 16. Further reduction of 11 (LAH) affords the saturated amines, 15. The stereochemistry for the formation of 15 is discussed using the torsion angle notation and the principal of least torsional distortion. In a one-pot reaction using LAH-acetic anhydride the lactams, 2, and the thiolactams, 10, are transformed into the enamides, 14. Compound 14 was also obtained from 11 by direct acetylation with acetic anhydride in the presence of triethylamine.     

Decomposition of polypropylene hydroperoxide by hindered amines

The hindered amine-induced decomposition of polypropylene hydroperoxide was studied in the solid state and in the presence of a liquid solvent and the polymer was compared with model hydroperoxides. The high reactivity of the macrohydroperoxides appears to be related to the adjacent, hydrogen-bonded hydroperoxide groups that occur in the polymer. The hindered amines are converted to nitroxides in the reaction via hydroxylamine intermediates. Amine-induced decomposition of polypropylene hydroperoxide is faster in the absence of a liquid solvent for the amine than in the presence of the solvent, probably because of the strong amine-hydroperoxide association that occurs in the solid state. The decomposition process in the solid state is sufficiently rapid for the reaction to contribute to the effectiveness of hindered amines in the light stabilization of polymers.     

Rapid ion-exchange chromatography for preparative separation of proteins. IV. Application to bovine carbonic anhydrase III from skeletal muscle.

Bovine muscle carbonic anhydrase III was purified to homogeneity by the strategy of rapid ion-exchange chromatography. The ionic exchanger used was CM-cellulose, and this is the first application of this technique on a cation exchanger. Nitrogen gas was used to pressurize the chromatographic column to accelerate the elution. The results show that proteins with high isoelectric points can also be purified in this way. The procedure is very time-saving compared with conventional chromatography, reducing the elution time five- to ten-fold. The proteins are in addition protected against oxidation by air.     

Enamine chemistry—XXV: Reduction of enaminones by LiAlH4 and NaBH4. Synthesis of α,β-unsaturated aldehydes

Cyclohexanone, 2-methyl-cyclohexanone and 4-methyl-cyclohexanone, 1, were transformed into the enaminones 4a–4e by the following two routes: (A): Acylation of the enamines, 2, derived from 1 and secondary amines (pyrrolidine, morpholine and piperidine) by ethyl chloroformate, and (B): Condensation of 1 with diethyl oxalate, giving the β-ketoesters 3, followed by reaction with the secondary amines. Ethyl 2(-1-pyrrolidinyl)-1-cyclopentene-1-carboxylate, 4f, and methyl 3-(1-pyrrolidinyl)-2-butenoate, 4g, were prepared from ethyl 2-oxo-1-cyclopentanecarboxylate and ethyl 3-oxo-butanoate, respectively, by condensation with pyrrolidine. Reduction of 4a by LAH afforded 1-cyclohexen-1-carboxaldehyde, 5a, 1-cyclohexene-1-methanol, 6a, and 1-(1-cyclohexene-1-methyl)pyrrolidine, 7a, in yields depending on the molar ratio of LAH/4a. Reduction of 4f by LAH gave cyclopentene-1-methanol, 6b, 1-(1-cyclopentene-1-methyl)pyrrolidine, 7b, and ethyl-2(1-pyrrolidinyl)-1-cyclo-pentanecarboxylate, 8b. Compound 4g, when reduced with LAH, yielded methyl 3-(1-pyrrolidinyl) butanoate, 8c (main product) and 1-(2-butenyl)pyrrolidine, 7c (minor). Reduction of 4 by NaBH₄ afforded exclusively the saturated β-aminoesters, 8 in high yields. The reductions with LAH and NaBH₄ are rationalized in terms of the HSAB principle.     

Dynamic fluorescence microscopy as a feasible technique for estimating the diffusion coefficients of small particles in the presence of additives

The Brownian motion of carboxylated polystyrene latex, labeled with fluorescent probe molecules, at low concentrations in aqueous solutions was investigated by dynamic fluorescence microscopy. For all three latex radii, i.e., 0.5, 0.265, and 0.1 mum, the estimated diffusion coefficients correspond well with the theoretical predictions if thermal and electrostatic contributions are included in the discussions. It was also possible to discriminate latex interactions with an added polymer. Added polyethylene glycol showed no or very weak interaction with the latex until the polymer overlap concentration was reached, at which the formation of a polymer network slowed down the latex diffusion. Polyvinylpyrrolidone, on the other hand, had a more pronounced interaction with the polystyrene latex and slowed down the diffusion even at polymer concentrations in the ppm range. The overall conclusion is that fluorescence microscopy is a feasible method for the study of the dynamic behavior of small particles in solution.