Aldehydes, reductive alkylation

Method 3. Reductive alkylation reaction of an amine or ammonia and hydrogen with an aldehyde or ketone over a hydrogenation catalyst. 

The dimethoxybenzyl group was used for backbone protection of the pseudopeptides of the form Xaai/r(CH2N)Gly (Xaa = amino acid). It is introduced by reductive alkylation with the aldehyde and NaCNBH3. Acidolysis with TFMSA in TFA/thioanisole is used to remove it from the amine, but the efficiency is dependent upon the peptide sequence. ... 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

The reductive capability of CgK has been a subject of interest (LA). Uses for CgK include the reductive cleavage of carbon-sulfur bonds (S5), the reductive alkylation of nitriles and esters (S6), and the reductive alkylation of aldehydes and ketones (S7). The activity of CgK has... 

Amides are very weak nucleophiles, far too weak to attack alkyl halides, so they must first be converted to their conjugate bases. By this method, unsubstituted amides can be converted to N-substituted, or N-substituted to N,N-disubstituted, amides. Esters of sulfuric or sulfonic acids can also be substrates. Tertiary substrates give elimination. O-Alkylation is at times a side reaction. Both amides and sulfonamides have been alkylated under phase-transfer conditions. Lactams can be alkylated using similar procedures. Ethyl pyroglutamate (5-carboethoxy 2-pyrrolidinone) and related lactams were converted to N-alkyl derivatives via treatment with NaH (short contact time) followed by addition of the halide. 2-Pyrrolidinone derivatives can be alkylated using a similar procedure. Lactams can be reductively alkylated using aldehydes under catalytic hydrogenation... 

Aldehydes and ketones have been converted to sulfides by treatment with thiols and pyridine-borane, RCOR -I- R"SH —+ RR CHSR", in a reductive alkylation reaction, analogous to 16-6. 

An attractive alternative to these novel aminoalcohol type modifiers is the use of 1-(1-naphthyl)ethylamine (NEA, Fig. 5) and derivatives thereof as chiral modifiers [45-47]. Trace quantities of (R)- or (S)-l-(l-naphthyl)ethylamine induce up to 82% ee in the hydrogenation of ethyl pyruvate over Pt/alumina. Note that naphthylethylamine is only a precursor of the actual modifier, which is formed in situ by reductive alkylation of NEA with the reactant ethyl pyruvate. This transformation (Fig. 5), which proceeds via imine formation and subsequent reduction of the C=N bond, is highly diastereoselective (d.e. >95%). Reductive alkylation of NEA with different aldehydes or ketones provides easy access to a variety of related modifiers [47]. The enantioselection occurring with the modifiers derived from NEA could be rationalized with the same strategy of molecular modelling as demonstrated for the Pt-cinchona system. 

Reductive alkylation of N-alkylglucamines with a variety of aldehydes or ketones in the presence of Pd/carbon provides the corresponding N,N-dialkylglucamines in high yield. Only minor amounts of aldol byproducts are formed. 

In conclusion, N,N-dialkylglucamines are prepared in high yield and purity by palladium-catalyzed reductive alkylation of an N-alkylglucamine with an aldehyde or ketone. A wide variety of 1 with moderate to very high hydro-phobicity are readily accessible. 

Aldol reaction of the aldehyde with itself In some instances, dehydration of the aldol and subsequent hydrogenation of the double bond was also observed, as was reductive alkylation of the monoalkylglucamine by aldol-derived aldehydes. 

Osmium tetroxide used in combination with sodium periodate can also effect alkene cleavage.191 Successful oxidative cleavage of double bonds using ruthenium tetroxide and sodium periodate has also been reported.192 In these procedures the osmium or ruthenium can be used in substoichiometric amounts because the periodate reoxidizes the metal to the tetroxide state. Entries 1 to 4 in Scheme 12.18 are examples of these procedures. Entries 5 and 6 show reactions carried out in the course of multistep syntheses. The reaction in Entry 5 followed a 5-exo radical cyclization and served to excise an extraneous carbon. The reaction in Entry 6 followed introduction of the allyl group by enolate alkylation. The aldehyde group in the product was used to introduce an amino group by reductive alkylation (see Section 5.3.1.2). 

The reduction of nitrobenzene to aniline is a major industrial process at the heart of the production of polyurethanes, and it is also often used as a marker reaction to compare activities of catalysts [1,2], It can be performed over a variety of catalysts and in a variety of solvents. As well as its main use in polymethanes, aniline is used in a wide range of industries such as dyes, agrochemicals, by further reaction and functionalisation. Reductive alkylation is one such way of functionalising aromatic amines [3, 4], The reaction usually takes place between an amine and a ketone, aldehyde or alcohol. However it is possible to reductively alkylate direct from the nitro precursor to the amine and in this way remove a processing step. In this study we examined the reductive alkylation of nitrobenzene and aniline by 1-hexanol. 

Chamow, S.M., Kogan, T.P., Venuti, M., Gadek, T., Harris, R.J., Peers, D.H., Mordenti, J., Shak, S., and Ashkenazi, A. (1994) Modification of CD4 immunoadhesin with monomethoxypoly (ethylene glycol) aldehyde via reductive alkylation. Bioconjugate Chem. 5, 133-140. 

The reductive alkylation of amines is called the Leuckart-Wallach reaction [112-115]. The primary or secondary amine reacts with the ketone or aldehyde. The formed imine is then reduced with formic acid as hydrogen donor (Scheme 20.27). When amines are reductively methylated with formaldehyde and formic acid, the process is termed the Eschweiler-Clarke procedure [116, 117]. 

Sodium cyanoborohydride NaBIpCN in methanol is the reagent of choice for the reductive alkylation of ammonia, primary aliphatic and aromatic amines and secondary aliphatic amines with aldehydes and relatively unhindered ketones (equation 53). 

Scheme 25 Cathodic reduction of activated aliphatic carboxylic acids to aldehydes (R alkyl, yields 70-82%) and ketones (R benzyl, yields 66- 72%).

Scheme 26 Cathodic reduction of aliphatic carboxylic acids in the presence of triphenylphosphineto aldehydes R alkyl, aryl, yields 36 -100%.

Scheme 27 Cathodic reduction of amino acids in the presence of triphenylphosphine to amino aldehydes R alkyl, yields 81-84%.

Another type of N-alkylation was achieved by the [IrCl(cod)]2-catalyzed reductive alkylation of secondary amine with aldehyde and silane (Equation 10.29) [53], For example, the treatment of dibutylamine 117 with butyraldehyde 118 and EtsSiH 119 (a 1 1 1 molar ratio amine, aldehyde and silane) or polymethyUiydrosiloxane (PMHS) in 1,4-dioxane at 75 °C under the influence of a catalytic amount of [lrCl(cod)]2, gave tributylamine 120. 

After epoxidation of the terminal olefin in syn-89 the pyrrolidine 91 was formed by reductive cleavage of the Cbz-protection and concomitant Sn2 cyclization of the free amine to epoxide 90. In five additional steps (+)-preus-sin (2) was synthesized with an overall yield of 19%. After AT-methoxycar-bonylation and oxidation of the alcohol to an aldehyde the alkyl side chain was introduced by a Wittig reaction. 

Treatment of aldehydes or ketones with ammonia, primary or secondary amines in reducing media is called reductive alkylation (of ammonia or amines) or reductive amination (of aldehydes or ketones). Reducing agents are most frequently hydrogen in the presence of catalysts such as platinum, nickel or Raney nickel [955], complex borohydrides [705, 954, 955], formaldehyde or formic acid [522]. 

Reductive methylation is achieved by the reaction of formaldehyde with ammonium chloride. It is carried out by heating the components at 100-120° and gives mono-, di- and trimethylamine in high yields (Eschweiler reaction) [312, 962]. No catalyst is needed part of the formaldehyde provides the necessary hydrogen while the other part is oxidized to formic acid. The same reaction can be applied to methylation of primary and secondary amines [962]. Reductive alkylation can also be accomplished by reducing mixtures of amines with acids which are first reduced to aldehydes (p. 171). 

Reduction = gain of electrons. Alkene, alkyne, aldehydes, ketones, alkyl halides, nitriles, carhoxylic acid and its derivatives, and benzene and its derivatives. 

To keep the probe specifically at the primary amine side chains, we have used pyrenecarboxaldehyde and attached it covalently to polyethylenimine by reduction with sodium borohydride of the Schiff base formed between the probe aldehyde and the polymer primary amine. Such reductive alkylation has been used widely with primary amines of enzymes.43,44 For three different adducts to the polymer, the extent of coupling with pyrene, expressed relative to units of monomer residues,... 

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