Piperidine catalyst

Five experimental procedures employing sodium alkoxide or piperidine Catalysts are compared for a number of varied condensations, Secondary amines are mild catalysts which seldom lead to by-products but which do not always effect condensation. Sodium erhoxide catalyst sometimes gives rearranged products. Potassium hydroxide in acetal solvents is the most convenient reagent for a number of condensations." ... 

Tetramethylpyrazine, p-dimethylaminobenzaldehyde, and 37% hydrochloric acid have been shown to give 2,3,5,6-tetra(p-dimethylaminostyryl)pyrazine (713). Similar condensations have also been applied to quarternary salts ofmethylpyrazines with a piperidine catalyst (714). Thus 1,2,5-trimethylpyrazinium methylsulfate and benzaldehyde gave 1,5-dimethyl-2-styrylpyrazinium methylsulfate. 

Two hexafluoroacetone-hydrogen cyanide adducts have been characterized previously, viz. the cyanohydrin (58) (from piperidine-catalysed reaction) and the 2 1 adduct 2,2,5,5-tetrakistrifluoromethyl-4-oxazolidinone (59) [from (CFs)aCO-NaCN-MeCN]. It has now been reported that large transparent crystals of the 3 2 adduct (60) separate from a sample of the cyanohydrin (58) when it is stored for more than 1 year this new adduct is more readily prepared from the cyanohydrin by treating it with an excess of hexafluoroacetone in the presence of DABCO at 100 °C for 16 h (or DABCO alone at 25 °C for a prolonged period ). Addition of an excess of the ketone to hydrogen cyanide (KCN catalyst) or to preformed cyanohydrin (58) (piperidine catalyst) gives a new 3 1 adduct (61) (>93%) and not the 3 2 adduct (60). Adduct (61) can be distilled at reduced pressure, but pyrolysis in the presence of cone. H2SO4 (trace) affords a mixture of... 

Ammonia Dibutyltin maleate Dibutyltin oxide Fluorosulfonic acid Phosphine Sodium ethylate Sodium hydride Tetrabutyl titanate Tetraisopropyl titanate p-Toluene sulfonic acid Zirconium butoxide catalyst, condensation reactions Dibutyltin diacetate Piperidine catalyst, conductive polymers Iron (III) toluenesulfonate catalyst, conversion of acetylene to acetaldehyde Mercury sulfate (ic) catalyst, copolymerization Di butyl ether catalyst, cracking Zeolite synthetic... 

In 2006, Fadda et al. reported the piperidine-catalyzed reaction of l-chloro-3,4-dihydronaphthalene-2-carboxalde-hyde 53 with pyrazole 52 and malonodinitrile 21 to provide an access to a chromeno[2,3-c]pyrazole 55 at high temperatures (Scheme 13.17) [28]. Exchange of the piperidine catalyst by an excess of ammonium acetate led to the formation of a pyrazolo[3,4-b]quinoline derivative 54 instead. 

It is now applied more widely to include malonic acid derivatives, such as diethyl monoethyl-malonate, ethyl cyanacetate, etc. Various amines may be used as catalysts, and usually the most effective is piperidine (hexahydro-pyridine) a mixture of piperidine and pyridine, or pyridine alone, is also often used. 

Knoevenagel reaction. The condensation of an aldehyde with an active methylene compound (usually malonic acid or its derivatives) in the presence of a base is generally called the Knoevenagel reaction. Knoevenagel found that condensations between aldehydes and malonic acid are effectively catalysed by ammonia and by primary and secondary amines in alcoholic solution of the organic amines piperidine was regarded as the best catalyst. 

The addition of active methylene compounds (ethyl malonate, ethyl aoeto-acetate, ethyl plienylacetate, nltromethane, acrylonitrile, etc.) to the aP-double bond of a conjugated unsaturated ketone, ester or nitrile In the presence of a basic catalyst (sodium ethoxide, piperidine, diethylamiiie, etc.) is known as the Michael reaction or Michael addition. The reaction may be illustrated by the addition of ethyl malonate to ethyl fumarate in the presence of sodium ethoxide hydrolysis and decarboxylation of the addendum (ethyl propane-1 1 2 3-tetracarboxylate) yields trlcarballylic acid ... 

Like butadiene, allene undergoes dimerization and addition of nucleophiles to give 1-substituted 3-methyl-2-methylene-3-butenyl compounds. Dimerization-hydration of allene is catalyzed by Pd(0) in the presence of CO2 to give 3-methyl-2-methylene-3-buten-l-ol (1). An addition reaction with. MleOH proceeds without CO2 to give 2-methyl-4-methoxy-3-inethylene-1-butene (2)[1]. Similarly, piperidine reacts with allene to give the dimeric amine 3, and the reaction of malonate affords 4 in good yields. Pd(0) coordinated by maleic anhydride (MA) IS used as a catalyst[2]. 

Tetrahydrofurfuryl alcohol reacts with ammonia to give a variety of nitrogen containing compounds depending on the conditions employed. Over a barium hydroxide-promoted skeletal nickel—aluminum catalyst, 2-tetrahydrofurfur5iarnine [4795-29-3] is produced (113—115). With paHadium on alumina catalyst in the vapor phase (250—300°C), pyridine [110-86-1] is the principal product (116—117) pyridine also is formed using Zn and Cr based catalysts (118,119). At low pressure and 200°C over a reduced nickel catalyst, piperidine is obtained in good yield (120,121). 

Isomerization is faciUtated by esterification at temperatures above 200°C or by using catalysts, such as piperidine and morpholine (6), that are effective in raising isomerization of fumarate to 95% completion. Resins made by using fumaric acid are exclusively fumarate polymers, demonstrate higher reactivity rates with styrene, and lead to a complete cross-linking reaction. 

Organic amines, eg, pyridine and piperidine, have also been used successfully as catalysts in the reactions of organosilanes with alcohols and silanols. The reactions of organosilanes with organosilanols lead to formation of siloxane bonds. Nickel, zinc, and tin also exhibit a catalytic effect. 

Ethylamines. Mono-, di-, and triethylamines, produced by catalytic reaction of ethanol with ammonia (330), are a significant outlet for ethanol. The vapor-phase continuous process takes place at 1.38 MPa (13.6 atm) and 150—220°C over a nickel catalyst supported on alumina, siUca, or sihca—alumina. In this reductive amination under a hydrogen atmosphere, the ratio of the mono-, di-, and triethylamine product can be controlled by recycling the unwanted products. Other catalysts used include phosphoric acid and derivatives, copper and iron chlorides, sulfates, and oxides in the presence of acids or alkaline salts (331). Piperidine can be ethylated with ethanol in the presence of Raney nickel catalyst at 200°C and 10.3 MPa (102 atm), to give W-ethylpiperidine [766-09-6] (332). 

Piperidine, l-(2-hydroxythiobenzoyI)-neutron diffraction, 2, 116 Piperidine, 4-hydroxy-2,2,6-trimethyI-as local anaesthetic, 1, 179 Piperidine, JV-methoxycarbonyl-electrolytic oxidation, 2, 374 Piperidine, 2-methyl-synthesis, 2, 524 Piperidine, 3-methyI-mass spectrometry, 2, 130 Piperidine, C-methyl-NMR, 2, 160 Piperidine, JV-methyl- C chemical shifts, 2, 15 catalyst... 

The striking effect of the catalyst is exemplified by the reaction of pregna-4, 16-diene-3,20-dione (10) with benzyl mercaptan. In the presence of piperidine only conjugate addition occurs to give (11) whereas with pyridine hydrochloride only the 3-benzyl thioenol ether (12) is formed. In the presence of p-toluenesulphonic acid both reactions take place to yield (13). 

The dimethyl acetal (94) is readily prepared from the 22-aldehyde (93) by direct reaction with methanol in the presence of hydrogen chloride. Ena-mines (95) are formed without a catalyst even with the poorly reactive piperidine and morpholine.Enol acetates (96) are prepared by refluxing with acetic anhydride-sodium acetate or by exchange with isopropenyl acetate in pyridine.Reaction with acetic anhydride catalyzed by boron trifluoride-etherate or perchloric acid gives the aldehyde diacetate. 

Additional evidence that a dynamic equilibrium exists between an enamine, N-hemiacetal, and aminal has been presented by Marchese (41). It should be noted that no acid catalysts were used in the reactions of aldehydes and amines discussed thus far. The piperidino enamine of 2-ethylhexanal (0.125 mole), morpholine (0.375 mole), and p-toluene-sulfonic acid (1.25 x 10 mole) diluted with benzene to 500 ml were refluxed for 5 hr. At the end of this time the enamine mixture was analyzed by vapor-phase chromatography, which revealed that exchange of the amino residue had occurred in a ratio of eight morpholine to one piperidine. Marchese proposed a scheme [Eqs. (4), (5) and (6)] to account for these... 

According to the Friedlander method, the condensation of the readily available 2-aminoiiicotinic aldehyde (20a) (74JOC726) or its 6-phenyl derivative (20b) [66JCS(C)315] with nitroacetic acid (21) in boiling ethanol with piperidine as catalyst is another example of this method, which affords in fair yields the corresponding 3-nitro-l,8-naphthyridin-2(lFI)-ones (22a, 74%) and (22b, 47%), respectively [66JCS(C)315]. 

A series of 2-aryloxazolo[4,5-/i]quinoline-5-arylidines was prepared by the reaction of 5,7-diamino-8-hydroxyquinoline with aromatic or aliphatic aldehydes in the presence of a basic catalyst such as piperidine. On the other hand, 2-styryl-5-diacetylamino-oxazolo[4,5-/i]quinolines were prepared by interaction of 2-methyl-5-diacetylamino-oxazolo[4,5-/i]quinoline with aromatic aldehydes (77MI1, 82MI2) (Scheme 6). 

During this work the presence of small quantities of piperidine and -picoline were also noticed. The exact mode of formation of these products remains to be elucidated, but the formation of piperidine shows that sufficient hydrogen remains on the catalyst to bring about some hydrogenation of the pyridine. 

Under the circumstance of catalytic hydrogenation of piperidine derivatives 190 in MeOH over Pd/C catalyst afforded an isomeric mixture of perhydropyrido[l,2-c]pyrimidines 174-177 (98TL7021, 00JA5017). The main product was 174 (66%). 

Catalytic hydrogenation of 2-cyano-l-(2-nitrophenyl)piperidines over Pearlman s catalyst in a low-pressure hydrogenator under 1 atm of hydrogen in dioxane gave cyclic amidine A -oxides 352 (01EJOC987). 

The precise structure of the zirconium catalyst was examined by NMR analysis. When Zr(Ot-Bu)4 (1 equiv), 8b (2 equiv), and NMI (3 equiv.) were combined in benzene-dg at 23 °C, two independent species which were assigned to a new zirconium catalyst and free 8b were observed. Although the signals of free 8b were still observed when Zr(Ot-Bu)4 (1 equiv), 8b (1 equiv), and NMI (3 equiv.) were stirred at 23 °C, only the signals assigned to the new zirconium catalyst were detected when the mixture was stirred at 80 °C for 2.5 h. These results indicated the formation of 9b as the new zirconium catalyst. The structure was also supported by an experiment in which Zr(Ot-Bu)4 (0.2 equiv), 8a (0.2 equiv), NMI (0.6 equiv), and MS 3 A were combined in benzene and the mixture was stirred for 2.5 h at 80 °C (formation of 9a). Imine Id (1 equiv.) and 7a (1.2 equiv.) were then added to the catalyst solution, and the mixture was stirred for 48 h at 23 °C. After the same work-up procedures as described above, the desired piperidine derivative was obtained in >98% yield with 89% ee, values comparable with those... 

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