Piperidine, catalysed

Acid depurination will also lead to DNA cleavage at guanine and adenine though it does not distinguish between the two. Protonation of the purines at pH 2 results in depurination as a consequence of the hydrolysis of the glycosidic bond and a piperidine catalysed -elimination of the phosphates then serves to break the DNA at that point. 

The introduction of a phenylseleno group on the a-carbon followed by peroxide oxidation to give the triethyl ester of 2-phosphonopropenoic acid is an alternative to the piperidine-catalysed condensation of triethyl phosphonoacetate with formaldehyde as examples of the conversion of an a-sp -carbon into an a-sp -carbon. 

Dithiobenzoates PhCS2R (R = allyl, propargyl, or benzyl) add to dimethyl acetylenedicarboxylate to form the dithioles (288) with migration of the group R. Piperidine catalyses the addition of acetylenic ketones Ar COC=CAr to 4-methylbenzene-l,2-dithiol to give the benzodithioles (289). The reaction of the acetal BrCH2CH(OEt)2 with ethanedithiol yields a mixture of the bis(dithiolan) (291) and derivatives of dithian, which are formed, respectively, from the cations (290) and (292). ... 

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... 

Aziridinium salts have been proposed as intermediates in a number of reactions. The piperidine-catalysed Knoevenagel condensation between benzaldehyde and bis(ethylsulphonyl)methane gives unexpected rearrangement products, possibly via the spiro-salt (529). The bicyclic aziridinium... 

Figure 3. Reaction of 2,4-dinitroanisole with piperidine, catalysed by...

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. 

Another competing cyclisation during peptide synthesis is the formation of aspartimides from aspartic acid residues [15]. This problem is common with the aspartic acid-glycine sequence in the peptide backbone and can take place under both acidic and basic conditions (Fig. 9). In the acid-catalysed aspartimide formation, subsequent hydrolysis of the imide-containing peptide leads to a mixture of the desired peptide and a (3-peptide. The side-chain carboxyl group of this (3-peptide will become a part of the new peptide backbone. In the base-catalysed aspartimide formation, the presence of piperidine used during Fmoc group deprotection results in the formation of peptide piperidines. 

The reaction is catalysed by added base (piperidine). These individual dependences were combined (at 40 °C) to give... 

The pincer complexes 89-90 (Fig. 2.14) catalyse the intramolecular hydroamination/ cyclisation of unactivated alkenes, yielding pyrrolidines and piperidines (n = 1,2, respectively). The reactions can be carried out in benzene or water with high... 

Hydroamination of activated alkenes has been reported with complexes 91-93 (Fig. 2.15). For example, 91 catalyses the hydroamination of methacrylonitrile (X = CN in Scheme 2.13) by a range of secondary amines (morpholine, thiomorpholine, piperidine, iV-methylpiperazine or aniline) in good to excellent conversions (67-99%) and anfi-Markovnikov regioselectivity (5 mol%, -80°C or rt, 24-72 h). Low enantioselectivies were induced ee 30-50%) depending on the amine used and the reaction temperature [79]. 

Substitution reactions of allylic nitro compounds often lead to rearranged products, as in palladium(0)-catalysed aminations and alkylations. Thus treatment of the nitro ester 419 with piperidine in the presence of tetrakis(triphenylphosphine)palladium yields a mixture of the unrearranged and rearranged amines 420 (R = piperidin-l-yl) and 421... 

The authors presume that the observed effect is due to acid catalysis by methanol, but no catalysis by phenol was observed. Pietra and Vitali111 have shown earlier that phenol catalyses the reaction of l-fluoro-2,4-dinitrobenzene with piperidine in benzene. 

Catalysis by DABCO in the reactions of FDNB with piperidine, r-butylamine, aniline, p-anisidine and m-anisidine (usually interpreted as base catalysis as in Section B) was also assumed to occur by the formation of a complex between DABCO and the substrate14913. The high (negative) p-value of —4.88 was deemed inappropriate for the usually accepted mechanism of the base-catalysed step (reaction 1). For the reactions with p-chloroaniline, m- and p-anisidines and toluidines in benzene in the presence of DABCO a p-value of —2.86 was found for the observed catalysis by DABCO (fc3DABC0). The results were taken to imply that the transition state of the step catalysed by DABCO and that of the step catalysed by the nucleophile have similar requirements, and in both the nucleophilic (or basicity) power of the nucleophile is involved. This conclusion is in disagreement with the usual interpretation of the base-catalysed step. 

Since morpholine and piperidine are stereochemically similar but exhibit different pKa values, the difference between their rates in the reactions of the fluoro-substrates in acetonitrile could be also due to a change in mechanism, whereby proton transfer from the intermediate 1 in equation 1 becomes rate-limiting when the reagent is morpholine. The change from an uncatalysed to a base-catalysed reaction with decrease in basicity of the nucleophile is well known in ANS for both primary and secondary amines1 200. 

Fustero has devised an intramolecular version of the iminium ion catalysed conjugate addition of nitrogen in the preparation of a series of simple pyrrolidine and piperidine derivatives [115]. The reactions proceed in chloroform to give the target heterocycles in good yield and excellent levels of stereocontrol (Scheme 32). 

In the ruthenium catalysed carbonylation of piperidine (60 °C, 10 bar CO) the catalyst precursor, [Ru3(CO)i2] was found to be converted mainly to [Ru(CO)5], although IR absorptions due to other minor species were also observed [94]. A catalytic mechanism was tentatively proposed, which involved [RuCO)4] as the active... 

Synthesis of the benzopyran ring has also been performed by microwave-assisted copper-catalysed cross coupling of an aryl iodide with terminal alkynes, in the presence of copper(I) iodide/triphenylphosphine (Scheme 3.35)56. An alternative approach involving microwave heating of mixtures of salicylaldehyde and various derivatives of ethyl acetate in the presence of piperidine has enabled rapid Knoevenagel synthesis of coumarin derivatives (Scheme 3.35)57. 

Trifluoroacetylacetone (152) reacts by a condensation reaction 30 with aromatic aldehydes218 in the presence of piperidine and acetic acid, in benzene. Triethylamine does not catalyse this reaction. Probably, the product 153 is obtained via the carbinolamine (154), which in turn yields the carbonyl group of the aldehyde. Obviously, the tertiary amine cannot displace a proton and the interaction forms a zwitterionic adduct (see 148). 

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