Piperidine reaction with benzaldehyde

The same reaction sequence performed in methanol affords a mixture of diastereo-mers of the phosphorylated phosphinic ester 48b, of which one pure isomer can be isolated32 . In the presence of piperidine, reductive elimination of nitrogen 28,29) from 45 to give bis(diphenylphosphoryI)methane competes with the prevailing formation of the phosphinic piperidide 48c32). Expected trapping of 47 by [2 + 2]-cycloaddition with benzaldehyde fails to occur in place of 1,2k5-oxaphosphetanes, products are obtained which arise mainly by way of the benzoyl radical32,33). 

It has been shown3 that piperidine salts and not the free base act as the catalyst in the Rnoevenagel reaction. The checkers obtained only a 71% yield with benzaldehyde containing less than 0.2% of benzoic acid. 

In an attempt to couple halobenzaldehydes with amines, A1203 was pre-absorbed with the substituted benzaldehydes and imidazole or piperidine as a base and irradiated with microwaves. However, the corresponding benzylic alcohols and benzoic acids were unexpectedly obtained by the Cannizzaro route (Scheme 4.20). The products of Cannizzaro reactions were also obtained as the main products, when microwave-assisted condensation reactions of benzaldehydes with vinyl acetate using barium hydroxide as the catalyst were attempted40. 

B) 2PiCH3 +C6H5CHO (PiCH2)2CHC6Hs Both reactions are catalyzed by piperidine reaction (B) is run in pyridine, reaction (A) in aromatic solvents such as benzene or toluene, A series of monosubstituted benzaldehydes react similarly via reaction (A) (Ref 23) as do also terephthalaldehyde (Ref 23), and isophthal-aldehyde (Ref 117), both with two moles of TNT. A similar product could not be made from phthalaldehyde (Ref 117), and only traces of HNS were obtained from TNT and 2,4,6-trinitrobenzaldehyde (Ref 31)... 

The aldehydes 3 were synthesized either by Vilsmeyer formyladon of 2 or by reaction of 4-fluorobenzaldehyde with a secondary amine (20). The stilbenes 4 were formed from the corresponding 4-dialkylamino-benzaldehydes either by the Homer-Emmons reaction with 4-nitrobenzyl-(diethyl)phosphonate (prepared by the Arbuzov reaction of a-bromo-4-nitrotoluene) or with 4-methylsulfonylbenzyl(diethyl)phosphonate (prepared in three steps from 4-methylthiobenzylaicohol) (21). A few nitrostilbene compounds were synthesized by heating aldehyde 3 with 4-nitrophenylacetic acid in the presence of piperidine. 

Pyrido[ 1,2-a]pyrimidine-6-thione 231 was prepared in the reaction of pyridinethione 229 and benzylidenemalononitrile in boiling dioxane in the presence of a catalytic amount of piperidine [93JCR(S)8]. 6H-Pyrido[l, 2-a]pyrimidine-6-thione 231 was also obtained when pyridinethione 229 was reacted with benzaldehyde in the presence of a few drops of piperidine for 2 hours, and then condensation product 230 was reacted with malononitrile. 

Reactions of bispyridinium salts 318 with benzaldehydes in the presence of a catalytic amount of piperidine in DMF at 70-80 °C for 30-40 h yielded 1 -arylmethylene-3,4-dihydro-l H-pyrido[2,l -c] [1,4] thiazinium... 

When 1,2,3,4-tetrahydroisoquinoline is heated in acetic acid with benzaldehyde, 4-benzylisoquinoline can be isolated in 34% yield. It was suggested110 that, by analogy with the products obtained from the condensation of benzaldehyde with piperidine, the reaction proceeds through a 1,2-dihydroisoquinoline intermediate (Scheme V). 

Both - and -alkylazolium ions, like the 2- and 4-alkylazoles themselves, can also react with electrophilic reagents without initial complete deprotonation. They undergo the same types of reactions as the alkylazoles but under milder conditions, and these reactions can often be catalyzed by piperidine. Thus, in quaternized pyrazoles, 5-methyl groups react with benzaldehyde to give styryl derivatives. The methyl groups in quaternized isoxazoles are also reactive, and here piperidine is sufficient as catalyst (Scheme 124). 

Treatment of 1,3-benzoxathiole derivatives 87 with benzaldehydes in the presence of piperidine/acetic acid gives thioaurone derivatives 88. This reaction probably involves an oxidation step. These are also synthesized by the reaction of disulfide 89 with aldehydes (Equation 4) <2005T8648>. 

Asymmetric synthesis of 1,2-diol derivatives based on asymmetric aldol reactions of a-alkoxy silyl enol ethers with aldehydes has been developed. The reaction of (Z)-2-benzyloxy-l-(5)-ethyl-l-trimethylsiloxyethene with benzaldehyde was conducted in dichloromethane at -78 °C with a chiral promoter consisting of Sn(OTf)2, (5)-l-ethyl-2-[(piperidin-l-yl)methyl]pyrrolidine, and Bu2Sn(OAc)2, to afford the corresponding aldol adduct in 83 % yield with 99 % anti preference. The enantiomeric excess of anti aldol is 96 % [38a]. In the aldol reaction of several kinds of aldehydes, e.g. aromatic,... 

As described above, zeolites can also act as solid base catalysts when the Si Al ratio is low and the extra framework cation is a large one such as The most basic common exchanged zeolite is CsX. With this material the aldol condensation of cyclooctanone with benzaldehyde gave only the monobenzylidene compound (Eqn. 10.23) 5 while reactions using piperidine, m nesium oxide or amorphous cesium aluminosilicate gave both the mono- and di-benzylidene products(Eqn. 10.12). The smaller ketones, cyclohexanone and... 

Problem 26.3 (a) Malonic ester reacts with benzaldehyde in the presence of piperidine (a secondary amine. Sec. 31.12) to yield a product of formula C14H16O4. What is this compound, and how is it formed (This is an example of the Knoevenagel reaction. Check your answer in Problem 21.22 (f), p. 714.) (b) What compound would be obtained if the product of (a) w ere subjected to the sequence of hydrolysis, acidification, and heating (c) What is another way to synthesize the product of (b) ... 

The condensation reactions of di- and trinitro mesitylene and m-xylene also indicate that nitro groups lose their characteristic activating influence when they are flanked by two methyl groups. In the presence of piperidine, 4,6-dinitro-ra-xylene (XLVII) and 2,4,6-trinitro-m-xylene (XLVIII) will condense with benzaldehyde 22 (equations 4 and 5). When... 

Other applications include the Knoevenagel reaction under microwave irradiation in a solvent-free reaction. With this technique, benzaldehyde reacts in a few minutes with diethyl cyanomethylphosphonate in the presence of carefully controlled amounts of piperidine to give diethyl 1-cyano-... 

Condensation of diethyl 2-oxopropylphosphonate with benzaldehyde on heating in CgHg in the presence of piperidine was reported by Pudovik et al. in 1967 to give a 65% yield of diethyl 1-acetyl-2-phenylvinylphosphonate (Scheme 7.95). o The reaction was further repeated in toluene with diethyl 2-phenyl-2-oxoethylphosphonate, piperidine, and AcOH under azeotropical removal... 

The Knoevenagel reaction (Scheme 6.20) involves the reaction of aromatic aldehydes with a variety of molecules CH2XY. The groups X and Y may be the same or different, but are invariably electron withdrawing, so creating an activated methylene group from which the carbanion CHXY is produced. The reaction is usually carried out in pyridine solution, with piperidine as the basic catalyst. The reactions of benzaldehyde with propane-1,3-dinitrile [malononitrile, CH2(CN)2] and diethyl propane-1,3-dioate [diethyl malonate, CH.,(CO,Et)2] are illustrative. In both cases, manipulation of the CH=CX2 group in the product allows the synthesis of other compounds. 

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