Piperazine, reactions

Piperazine, reaction with diborane, 16 248 (3-Piperidinopropyl)diphenylsilanol, 42 193 Pivaloylchloride, reaction with disilylphos-phanes, 33 261... 

Both piperazine and N,N -dimethylethylenediamine form salts with nitrogen (II) oxide 22), The product of the piperazine reaction can be formulated as either... 

Significant quantities of amine and amide esters are formed by side reactions (9). In addition, with dialkanolamines, amide diesters, morpholines, and piperazines can be obtained, depending on the starting material. Reaction of dialkanolamines with fatty acids in a 2 1 ratio, at 140—160°C, produces a second major type of alkanolamide. These products, in contrast to the 1 1 alkanolamides, are water soluble they are complex mixtures of AJ-alkanolamides, amine esters, and diesters, and still contain a considerable amount of unreacted dialkanolamine, accounting for the water solubiUty of the product. Both the 1 1 and the 2 1 alkanolamides are of commercial importance in detergents. 

In a series of detailed studies, Armand and coworkers have examined the electrochemical reduction of pyrazines (72CR(C)(275)279). The first step results in the formation of 1,4-dihydropyrazines (85), but the reaction is not electrochemically reproducible. The 1,4-dihydropyrazine is pH sensitive and isomerizes at a pH dependent rate to the 1,2-dihydro compound (83). The 1,2-dihydropyrazine then appears to undergo further reduction to 1,2,3,4-tetrahydropyrazine (88) which is again not electrochemically reproducible. Compound (88) then appears to undergo isomerization to another tetrahydro derivative, presumably (8, prior to complete reduction to piperazine (89). These results have been confirmed (72JA7295). 

A number of reductive procedures have found general applicability. a-Azidoketones may be reduced catalytically to the dihydropyrazines (80OPP265) and a direct conversion of a-azidoketones to pyrazines by treatment with triphenylphosphine in benzene (Scheme 55) has been reported to proceed in moderate to good yields (69LA(727)23l). Similarly, a-nitroketones may be reduced to the a-aminoketones which dimerize spontaneously (69USP3453279). The products from this reaction are pyrazines and piperazines and an intermolecular redox reaction between the initially formed dihydropyrazines may explain their formation. Normally, if the reaction is carried out in aqueous acetic acid the pyrazine predominates, but in less polar solvents over-reduction results in extensive piperazine formation. 

Syntheses of piperazine derivatives by combining microbial and chemical reactions 99YGK466. 

The reaction of 5-methoxy-2(5//)-furanone 168 with amines was also studied (89T6799). The conjugated addition of ethanolamine to the furanone 168 gave the racemic amino lactone 275 (R = CH2CH20H). Similarly, piperazine reacted with two equivalents of 168 to provide the diadduct 276 as a single diastereomer (no traces of the other isomer were detected). With tryptamine, the reaction was nearly quantitative with the the formation the tran -adduct 277 (R = tryptophanyl) (Scheme 72) (89T6799). 

Condensation of the substituted phenethyl bromide, 18, with piperazine can be stopped at the monosubstituted amine (19). Reaction of this amine with propiophenone and formaldehyde in a Mannich reaction affords eprazinone (20) an antitussive agent. 

Treatment of a mixture of ortho anisidine and bis(2-hydroxy-ethyl) amine with hydrogen chloride affords the aryl-substituted piperazine, 171. (The first step in this reaction probably consists in conversion of at least one hydroxyl group to the chloride this then serves to alkylate the aromatic amine.) Alkyla-... 

Though dental afflictions constitute a very significant disease entity, these have received relatively little attention from medicinal chemists. (The fluoride toothpastes may form an important exception.) This therapeutic target Is, however, sufficiently Important to be the focus of at least some research. A highly functionalized piperazine derivative that has come out of such work shows prophylactic activity against dental caries. Condensation of the enol ether 1 of thiourea with ji-pentylisocyanate gives the addition product 1J. Reaction of this with diamine 78, derived from piperazine, leads to substitution of the methylthio moiety by the primary amine, in all likelihood by an addition-elimination sequence. There is thus obtained ipexidine (79). ... 

Alteration of the structural pattern produces a pair of adrenergic a-blocking agents which serve as anti hypertensives. These structures are reminiscent of prazoci n. Reaction of piperazine with 2-furoy1 chloride followed by catalytic reduction of the furan ring leads to synthon 69. This, when heated... 

Alfuzosin (91) is a prazosin-like hypotensive adrenergic a-1 receptor blocker with the special structural feature that two carbons have been excised conceptually from the piperazine ring normally present in this series. Following the usual sequence for this series, reaction of 4-amino-2-chloro-7-dimethoxyquinazoline (89) with the tetrahydro-2-furyl amide of 3-methylaminopropyla-mine (90) gives alfuzosin (91) [25], Alfuzosin is claimed to cause less orthostatic hypotention (dizziness or fainting upon sudden rising) than prazosin. 

The residue consists of crude 10-(3-chloropropyl)-2-acetylphenothiazine as a viscous oil and is used in the next step without further purification. The crude base obtained from the reaction of 10-(3-chloropropyl)-2-acetylphenothiazine with 1-(2-hydroxyethyl)piperazine is purified by conversion to its dimaleate salt, MP 167°-168.5° from ethanol. 

O.OB mol (19 g) of 4-chlorobenzhydryl chloride and 0.16 mol (16g) of methylpiperazine were mixed in about 20 cc of dry benzene. The flask containing the reaction mixture was covered by a watch glass and set in a steam bath, and heating was continued for 6 hours. The contents of the flask were partitioned between ether and water and the ethereal layer was washed with water until the washings were neutral. The ethereal layer was extracted successively with 30-and 10-cc portionsof 3 N hydrochloric acid. On evaporation of the ether layer there remained a residue of 2.5 g. The aqueous extracts were united and basified with concentrated alkali. The oily base was taken into ether and dried over potassium carbonate. On evaporation of the ether, N-methvl-N -(4-chlorobenzhvdryl) piperazine was recovered in the form of a viscous oil in 75% yield. The N-methvl-N -(4-chlorobenzhvdryl) piperazine was dissolved in absolute alcohol and ethanolic hydrogen chloride added in excess. The dihydrochloride crystallized... 

This compound can be prepared by the reaction of cinnamoyl chloride with benzhydryl-piperazine. The reaction is carried out in dry benzene under reflux. The benzene is then evaporated, the residue taken up in chloroform, washed with dilute HCI and then made alkaline. 

A mixture of 31 5 g (0.1 mol) of 2-chloro-9-(3 -dimethylaminopropylidene)-thiaxanthene (MP 97°C) and 100 g of N-( 3-hydroxyethyl)-piperazine is heated to 130°C and boiled under reflux at this temperature for 48 hours. After cooling, the excess of N-( 3-hydroxyethyl)-piperazine Is evaporated in vacuo, and the residue is dissolved in ether. The ether phase is washed with water and extracted with dilute acetic acid, and 2-chloro-9-[3 -N-(N - -hydroxy-ethyD-piperazinylpropylidene] -thiaxanthene separated from the aqueous acetic acid solution by addition of dilute sodium hydroxide solution to basic reaction. The free base is extracted with ether, the ether phase dried over potassium carbonate, the ether evaporated and the residue dissolved in absolute ethanol. By complete neutralization of the ethanolic solution with a solution of dry hydrogen chloride in absolute ethanol, the dihydrochloride of 2-chloro-9-[3 -N-(N -(3-hydroxyethyl)-piperazinylpropylidene] -thiaxanthene is produced and crystallizes out as a white substance melting at about 250°C to 260°C with decomposition. The yield is 32 g. 

By operating in this manner 10-(2-methyl-3-chloro-propyl)phenothiazine is obtained. A mixture of 10-(2-methyl-3-chloro-propyl)phenothiazine and 1-[2-(2-hydroxyethoxy)ethyl] piperazine is then heated at 110 -120°C for 20 hours. After cooling, the reaction product is dissolved in 200 cc of benzene and the solution washed several times with water. 

A) A mixture of 333 parts of 4-(1 -piperazinyDphenol dihydrobromide, 11.2 parts of acetic acid anhydride, 42 parts of potassium carbonate and 300 parts of 1,4-dioxane is stirred and refluxed for 3 days. The reaction mixture is filtered and the filtrate is evaporated. The solid residue is stirred in water and sodium hydrogen carbonate is added. The whole is stirred for 30 minutes. The precipitated product is filtered off and dissolved in a diluted hydrochloric acid solution. The solution is extracted with trichloromethane. The acid aqueous phase is separated and neutralized with ammonium hydroxide. The product is filtered off and crystallized from ethanol, yielding 5.7 parts of 1 acetyl-4-(4-hydroxyphenyl)piperazine MP 181.3°C. 

B) A mixture of 2.4 parts of 1 acetyl-4-(4-hydroxyphenyl)piperazine, 0.4 part of sodium hydride dispersion 78% 75 parts of dimethylsulfoxide and 22.5 parts of benzene is stirred for one hour at 40°C. Then there are added 4.2 parts of cis-2-(2,4-dichlorophenyl)-2-(1 H-imidazol-1 -ylmethyl)-1,3-dioxolan-4-ylmethyl methane sulfonate and stirring is continued overnight at 100°C. The reaction mixture Is cooled and diluted with water. The product is extracted with 1,1 -oxybisethane. The extract is dried, filtered and evaporated. The residue Is crystallized from 4-methyl-2-pentanone. The product is filtered off and dried, yielding 3.2 parts (59%) of cis-1-acetyl-4-[2-(2,4-dichlorophenyl)-2-(1 H-imidazol-1-ylmethyl)-13-di-oxolan-4-ylmethoxy] phenyl] piperazine MP 146°C. 

The sodium derivative of the 2-trifluoromethylphenothiazine was prepared from 26.7 g (0.1 mol) of 2-trifluoromethylphenothiazine and 2.3 g (0.1 g atom) of sodium in 500 ml of liquid ammonia. After the reaction was completed, the ammonia was driven off and 500 ml of dry toluene were added. A solution of 25 g (0.09 mol) of N-(3-chloropropyl)-N -[2-(1,3-dioxanyl)-ethyl] -piperazine In 200 ml of toluene was added drop by drop to this solution which was then refluxed with stirring for 1B hours. After cooling, the precipitate which had formed was filtered and the filtrate was washed with water, dried and concentrated in vacuo. 33 g of brown oil, the N-3-(2-trifluoromethyl-10-phenothiazinyl)-propyl-N -2-[2-(1,3-dioxanyl)] -ethyl-piperazine, were obtained. 

To this acid was then added 1 g of 4-ethyl-2,3-dioxo-1-piperazinocarbonyl chloride (from the reaction of N-ethylethylenediamine and diethyl oxalate to give 2,3-dioxo-4-ethyl-piperazine which Is then reacted with phosgene) and the resulting mixture was reacted at 15°C to 20°C for 2 hours. After the reaction, a deposited triethylamine hydrochloride was separated by filtration, and the filtrate was incorporated with 0.4 g of n-butanol to deposit crystals. The deposited crystals were collected by filtration to obtain 1.25 g of white crystals of 6-[ D(—l-Ct-(4-ethyl-2,3-dioxo-1 -piperazinocarbonylaminolphenylacetamido] penicillanic acid. Into a solution of these crystals in 30 ml of tetrahydrofuran was dropped a solution of 0.38 g of a sodium salt of 2-ethyl-hexanoic acid in 10 ml of tetrahydrofuran, upon which white crystals were deposited. The deposited crystals were collected by filtration, sufficiently washed with tetrahydrofuran and then dried to obtain 1.25 g of sodium salt of 6-[D(—)-a-(4-ethyl-2,3-di-0X0-1-piperazinocarbonylaminolphenylacetamido] penicillanic acid, melting point 183°C to 185°C (decomposition), yield 90%. 

To a solution of 17.2g (0.10 mol) of 3-bromopropionyl chloride in 100 ml of anhydrous benzene was added dropwise with stirring a solution of 8.6 g (0.10 mol) of anhydrous piperazine in 20 ml of dry chloroform over a period of 30 minutes. The temperature rose spontaneously to 45°C during the addition. After the temperature ceased to rise, stirring was continued for another hour. The reaction mixture was then filtered to remove the piperazine hydrochloride by-product. The filtrate was evaporated to dryness and the residue recrystallized from ethanol to obtain the desired N,N -bis-(3-bromopropionyl) piperazine as a white crystalline sol id melting at 103°C to 104°C. The identity of the product was further established by elemental analysis. 

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