Halo aldehydes, reduction

The yield of the more active RRR-a-tocopherol can be improved by selective methylation of the other tocopherol isomers or by hydrogenation of a-tocotrienol (25,26). Methylation can be accompHshed by several processes, such as simultaneous halo alkylation and reduction with an aldehyde and a hydrogen haUde in the presence of staimous chloride (27), amino alkylation with ammonia or amines and an aldehyde such as paraformaldehyde followed by catalytic reduction (28), or via formylation with formaldehyde followed by catalytic reduction (29). 

Although 3y5-hydroxy-A -l9-aldehydes can be obtained from the corresponding oxime by acid treatment, the most efficient method for the production of A -19-aldehydes is nitrosation of the oximes followed by zinc reduction of the 5a-halo hemiacetal. ... 

Reduction of a-halo sulfides In combination with Lil, CrCl2 reduces a-halo sulfides to (a-alkylthio)chromium compounds, which undergo selective 1,2-addition to aldehydes (equation I). The [l-(phenylthio)ethyl]chromium(III) reagent ob-... 

Preparation. The general preparation of u-hydroxy acids is by the hydrolysis of an a-halo acid or by Ihe acid hydrolysis of the cyanohydrins of an aldehyde or a ketone. 0-Hydroxy acids may be made by catalytic reduction of 0-keut esters followed by hydrolysis. 0-Hydroxy acids can also he prepared by ihe ReformaCsky reaction y-Hydroxy acids are seldom obtained in the free slate because of ihe case wilh which they form... 

Selective reduction of carbonyl groups.1 Heterogeneous reduction of carbonyl groups by triethoxysilane with CsF (or KF) as catalyst is highly selective, the reactivity order being aldehyde > ketone > ester. Double bonds, nitro, halo, and amido groups are inert to this reagent. 

Reduction of nitroalkenes. Vinyl nitro compounds are reduced to saturated ketones or aldehydes by Raney nickel and an aqueous solution of sodium hypophosphite. Ester groups, C=C bonds, and aryl NO, and halo groups are not reduced. Under these conditions nitroalkanes arc reduced to amines, and oximes are converted into carbonyl compounds in high yield. 

The reaction is most useful for the preparation of olefinic, halo, and nitro alcohols from the corresponding substituted aldehydes and ketones. These substituents ate very often affected by other reduction procedures. Excellent directions are found in the preparations of crotyl alcohol (60%), l-bromo-5-hexanol (64%), l-chloco-4-pentanol (76%), /S,/S,/S-trichloroethyl alcohol (84%), methyl-p-chlorophenylcarbinol (81%), and o-nitrobenzyl alcohol (90%). The reaction has also been used in the preparation of certain tetralols and decalols as well as 9-fluo-renylcarbinol (50%). The thiophene and furan nuclei are not reduced. 

A synthesis of nitriles from the cyanohydrins of aromatic aldehydes via the reduction of the corresponding a-halo cyanides has been proposed. As an example, benzaldehyde cyanohydrin is converted by the action of thionyl chloride to phenylchloroacetonitrile (80%). This substance is reduced with zinc in acetic acid to phenylacetonitrile (70%). ... 

Unsymmetrical secondary amines are readily prepared in good yields by the catalytic reduction of Schiff bases at moderate temperatures in high-or low-pressure equipment. Many examples have been cited. The intermediate imines are prepared from primary amines and aldehydes—very seldom from ketones—and may be used without isolation (cf. method 431). For the preparation of aliphatic amines, e.g., ethyl-w-propylamine and n-butylisoamylamine, a prereduced platinum oxide catalyst is preferred with alcohol as the solvent. Schiff bases from the condensation of aromatic aldehydes with either aromatic or aliphatic amines are more readily prepared and are reduced over a nickel catalyst. In this manner, a large number of N-alkylbenzylamines having halo, hydroxyl, or methoxyl groups on the nucleus have been made. Reductions by means of sodium and alcohol and lithium aluminum hydride have also been described,... 

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