Nitro aldehydes, aromatic, reduction preparation

This reaction has found little application to mercaptan syntheses since the mercaptans are usually as readily available (by other methods) as the disulfides. The S-S linkage is reduced by zinc in acetic or sulfuric " acid, lithium aluminum hydride, or metallic sodium. y-Hydroxy-propyl disulfide is reduced electrolytically in 70% yield. Reduction by sodium disulfide does not reduce the nitro group in the preparation of p-nitrothiophenol (65%), whereas zinc and acetic acid converts o-nitro-phenyl disulfide to o-aminothiophenol (90%). Disulfides made by the action of ammonium hydrogen sulfide on aldehydes are sources for difficultly available aromatic and heterocyclic mercaptans. The disulfides are reduced by aluminum amalgam and water. ... 

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-... 

Secondary amines can be prepared from the primary amine and carbonyl compounds by way of the reduction of the derived Schiff bases, with or without the isolation of these intermediates. This procedure represents one aspect of the general method of reductive alkylation discussed in Section 5.16.3, p. 776. With aromatic primary amines and aromatic aldehydes the Schiff bases are usually readily isolable in the crystalline state and can then be subsequently subjected to a suitable reduction procedure, often by hydrogenation over a Raney nickel catalyst at moderate temperatures and pressures. A convenient procedure, which is illustrated in Expt 6.58, uses sodium borohydride in methanol, a reagent which owing to its selective reducing properties (Section 5.4.1, p. 519) does not affect other reducible functional groups (particularly the nitro group) which may be present in the Schiff base contrast the use of sodium borohydride in the presence of palladium-on-carbon, p. 894. 

Boger s synthesis commenced with the preparation of the left-hand fi agment 155. A sequence of phenol protection of 151, aldehyde oxidation, Curtius rearrangement, tosylation, nitro reduction, Boc protection, and Pb(OAc)4 mediated oxidation afforded quinodiimide 152. A key Diels-Alder reaction gave 153 in good yield. Treatment of 153 in a sequence of oxonolysis, aromatization, Boc deprotection, cyclization to the lactam, A-tosyl removal, indole reduction, and selective Boc protection afforded 154. Conversion of the lactam to the... 

Hantzsch ester (2, R = Et) and an organocatalyst -benzyl isothiouronium chloride, prepared from thiourea, catalysed the reductive amination of aromatic, aliphatic, heterocyclic, and cyclic aldehydes to amines in high yields. Aliphatic aldehydes reacted with difficulty and required a higher temperature. Nitro, nitrile, and carbonyl moieties were not reduced. ... 

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