Pyridyl water

It is obvious that the reaction is accelerated markedly by water. However, for the first time, the Diels-Alder reaction is not fastest in water, but in 2,2,2-trifiuoroethanol (TFE). This might well be a result of the high Bronsted acidity of this solvent. Indirect evidence comes from the pH-dependence of the rate of reaction in water (Figure 2.1). Protonation of the pyridyl nitrogen obviously accelerates the reaction. 

In Chapter 2 the Diels-Alder reaction between substituted 3-phenyl-l-(2-pyridyl)-2-propene-l-ones (3.8a-g) and cyclopentadiene (3.9) was described. It was demonstrated that Lewis-acid catalysis of this reaction can lead to impressive accelerations, particularly in aqueous media. In this chapter the effects of ligands attached to the catalyst are described. Ligand effects on the kinetics of the Diels-Alder reaction can be separated into influences on the equilibrium constant for binding of the dienoplule to the catalyst (K ) as well as influences on the rate constant for reaction of the complex with cyclopentadiene (kc-ad (Scheme 3.5). Also the influence of ligands on the endo-exo selectivity are examined. Finally, and perhaps most interestingly, studies aimed at enantioselective catalysis are presented, resulting in the first example of enantioselective Lewis-acid catalysis of an organic transformation in water. 

Inspired by the work of Burk and Feaster ) we attempted to use (2-pyridyl)hydrazine (4.36) as a coordinating auxiliary (Scheme 4.10). Hydrazines generally react effidently with ketones and aldehydes. Hence, if satisfactory activation of the dienophile can be achieved through coordination of a Lewis acid to the (2-pyridyl)hydrazone moiety in water. Lewis-add catalysis of a large class of ketone- and aldehyde-activated dienophiles is antidpated Subsequent conversion of the hydrazone group into an amine functionality has been reported previously by Burk and Feaster ... 

In summary, the work in this thesis provides an overview of what can be achieved with Lewis-acid and micellar catalysis for Diels-Alder reactions in water as exemplified by the reaction of3-phenyl-l-(2-pyridyl)-2-propene-l-ones with cyclopentadiene. Extension of the observed beneficial effect of water on rates and particularly enantioselectivities to other systems is envisaged. 

Chapter 2 describes the results of the first detailed study of Lewis-acid catalysis of a Diels-Alder reaction in water. Substituted 3-phenyl-l-(2-pyridyl)-2-propen-l-one dienophiles (la-gin Scheme 1) were found to coordinate to Co, Cu" and Zn ions in aqueous solution. This process forms... 

The perchlorate ion, CIO , is considered to be noncoordinating ia the presence of water. When water is rigorously excluded, anhydrous complexes such as Ni(CH2CN) (C10 2> where n is 2, 4, or 6, can be prepared. Perchlorate complexes of Ni, Co, Cu, and Sn have been reported. In each case, however, an organic group such as CH CN, CH, or pyridyl is involved (73—76). 

A special type of ammonio group is represented by 4-( 1 -pyridinium)-pyridine and other azinium analogs. Such products often result from self-quaternization of highly reactive derivatives. A -(4-Pyridyl)-and A -(3-nitro-4-pyridyl)-pyridinium chloride hydrochlorides (121) react with aniline, chloride ion, and water to give 4-substituted pyridines plus pyridine. l-(2-Quinolyl)- and l-(4-quinolyl)-pyridinium salts undergo 2- and 4-substitution, respectively, with amines, anilines, hydroxylamine, phenols, alkoxides, mercaptans, and chloride... 

Preparation of Bisacodyl 5 grams of (4,4 -dihydroxy-diphenyl)-(pyridyl-2)-methane are heated with 5 grams of anhydrous sodium acetate and 20 cc of acetic anhydride for three hours over a boiling waterbath. The cooled reaction mixture is poured into water, whereby after a while a colorless substance precipitates, which Is filtered off with suction, washed with water and recrystallized from aqueous ethanol. Colorless bright crystals, MP 138°C are obtained. 

After having been cooled it is washed three times in water, three times in a 5% solution of caustic soda, and then another three times in water. The solution in xylene is dried over sodium sulfate and the xylene is completely distilled off in vacuo. Thus 11.0 parts of hexa-methylene-bis-(N-methyl carbamic acid-3-pyridyl ester) are obtained. 

The electrolysis is carried out at a reference potential of -2.4 volts vs a standard calomel electrode. An initial current density of 0.0403 amp/cm is obtained which drops to 0.0195 amp/cm at the end of the reduction, which is carried on over a period of 1,682 minutes at 15° to 20°C. The catholyte is filtered, the solid material is washed with water and dried. 430 g of the 2,3-bis-(3-pyridyl)-butane-2,3-diol is recrystallized from water, MP 244° to 245°C. 

According to U.S. Patent 2,676,964 to 1.0 mol of potassium amide in 3 liters of liquid ammonia, is added 1.0 mol of 2-benzylpyridine. After 15 minutes, 1.1 mols of 3reaction product decomposed with water and ether extracted. The ether layer is dried over Sodium sulfate and after evaporation the residue is distilled, giving the 3-phenyl-3-(2-pyridyl)-N,N-dimethylpropylamine, BP 139°-142°C/1-2 mm. The maleate is produced by reaction with maleic acid. 

Upon completion of the addition, the mixture is agitated for 7 hours at ambient temperature. The solution is then poured into 3 liters of water/ice obtaining a clear solution of dark yellow color which is rendered alkaline upon phenolphthalein with 30% NaOH and extracted with ethyl ether to eliminate the majority of the pyridine. The mixture is filtered with active charcoal, the pH adjusted to 8 with hydrochloric acid 1 1 and extracted with chloroform to remove the 4,4 -dihydroxydiphenyl-(2-pyridyl)-methane which has not reacted. 

To a solution of 60 g of potassium xanthogenate in 240 cc of water there is added dropwise, while being cooled with ice, a solution of 42 g of 3,4-bis-bromomethyl-4-hydroxy-5-methyl-pyridinium-bromide In 1 liter of water so that the temperature remains between 2°C and 5°C. After stirring for 1 hour at the same temperature, the water is decanted off and the residue is triturated with acetone. Yield 25 g of 4-hydroxymethyl-5-hydroxy-6-methyl-pyridyl-(3)-methy I xanthogenate melting point 170°C to 171°C (alcohol, decomposition). 

A mixture of 0.5 gram of platinum oxide and a solution of 2.0 grams (0.0067 mol) of 3,4-dihydroxyphenyl-2-pyridyl ketone hydrobromide in 20 ml of water and 80 ml of ethanol Is hydrogenated on the Parr apparatus using an initial hydrogen pressure of 50 psi at room temperature. The reaction mixture is filtered, the filtrate concentrated in vacuo and the residue triturated with acetone to give erythro-3,4-dihydroxyphenyl-2-piperidinylcarbinol hydrobromide, MP 210° to 211°C (decomposition). 

The mixture is poured onto excess ice, acidified with concentrated hydrochloric acid, the ether layer sepatated and extracted with water (1 x 200 cc). The combined aqueous extracts are washed with ether (1 x 200 cc) basified with 0.880 ammonia and extracted with chloroform (3 x 350 cc) the extract is washed with water (2 x 100 cc), dried over sodium sulfate, evaporated, and the residue extracted with boiling light petroleum (BP 60° to 80°C 10 volumes), filtered hot and evaporated to dryness. The residue is recrystallized from alcohol to give a cream solid (119 g, 80%), Pi/IP 117° to 118°C. Recrystallization gives 1-(4-methylphenyl)-1-(2-pyridyl)-3-pyrrolidonopropan-1-ol, MP 119° to 120°C. 

To 9 g of n-butyllithium in 200 ml of dry ether 20 g of 3-bromopyridine Is added as quickly as possible at -40°C without raising the temperature. When the addition Is finished the mixture is stirred for another 30 minutes. Thereafter 32.5 g of 0>dimethylamino-4 -bromopro-piophenone is added in such a way that the temperature does not exceed -40°C. The cooling is discontinued and the mixture is stirred during the night whereupon the reaction mixture is poured onto ice and diluted HCI, which is washed with ether and is extracted with 20 ml of methylene dichloride. The methylene dichloride is dried and evaporated. The crystals are dissolved in water, which then is made alkaline with a solution of Na2C03, is extracted with ether, dried, and evaporated and recrystallized from isopropyl ether, petroleum ether 1 1. Yield 4 g of 1 -(4 -bromophenyl)-3-(N,N-dimethylamino)-1 -(3"-pyridyl)-propanol. Melting point 67°C. 

The 7-bromo-5-(2-pyridyl)diazepinone 18 reacts with lead(IV) acetate to yield the 3-acetoxy derivative 19, which is converted into the 3-hydroxy compound 20 by the action of sodium methoxide, followed by water.201... 

Copper-complexes prepared with other type of N-chelating ligands have been also prepared and evaluated as catalysts for the Diels-Alder reaction. Eng-berts et al. [103] studied enantioselective Diels-Alder reaction of 3-phenyl-l-(2-pyridyl)-2-propen-l-one with cyclopentadiene in water (Scheme 39). By using coordinating chiral, commercially available a-amino-adds and their derivatives with copper salts as catalysts, they obtained the desired product with yields generally exceeding 90%. With L-abrine (72 in Scheme 39) as chiral moiety, an enantiomeric excess of 74% could be achieved. Moreover, the catalyst solution was reused with no loss of enantioselectivity. 

Forshey PA, Kuwana T. 1983. Electrochemistry of oxygen reduction. 4. Oxygen to water conversion by iron(II)(tetrakis(N-methyl-4-pyridyl)porphyrin) via hydrogen peroxide. 

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