Conjugated aldehydes 1,4-reduction

Aldol reaction of campholenic aldehyde with propionic aldehyde yields the intermediate conjugated aldehyde, which can be selectively reduced to the saturated alcohol with a sandalwood odor. If the double bond in the cyclopentene ring is also reduced, the resulting product does not have a sandalwood odor (161). Reaction of campholenic aldehyde with -butyraldehyde followed by reduction of the aldehyde group gives the aHyUc alcohol known commercially by one manufacturer as Bacdanol [28219-61 -6] (82). 

Conjugate addition of methyl magnesium iodide in the presence of cuprous chloride to the enone (91) leads to the la-methyl product mesterolone (92) Although this is the thermodynamically unfavored axially disposed product, no possibility for isomerization exists in this case, since the ketone is once removed from this center. In an interesting synthesis of an oxa steroid, the enone (91) is first oxidized with lead tetraacetate the carbon at the 2 position is lost, affording the acid aldehyde. Reduction of this intermediate, also shown in the lactol form, with sodium borohydride affords the steroid lactone oxandrolone... 

Pr)4, " borohydride-exchange resin,and formic acid. When the last is used, the process is called the Wallach reaction. Conjugated aldehydes are converted to alkenyl-amines with the amine/silica gel followed by reduction with zinc borohydride.In the particular case where primary or secondary amines are reductively methylated with formaldehyde and formic acid, the method is called the Esch-weiler-Clarke procedure. It is possible to use ammonium (or amine) salts of formic acid, " or formamides, as a substitute for the Wallach conditions. This method is called the Leuckart reaction,and in this case the products obtained are often the N-formyl derivatives of the amines instead of the free amines. Primary and secondary amines can be iV-ethylated (e.g., ArNHR ArNREt) by treatment with NaBH4 in acetic acid. Aldehydes react with aniline in the presence of Mont-morillonite KIO clay and microwaves to give the amine. Formaldehyde with formic acid converts secondary amines to the N-methyl derivative with microwave irradiation. 

Conjugate reductions and Michael Alkylations of conjugated aldehydes are listed in Section 74 (Alkyls from Alkenes). 

D. Conjugate Reduction of Conjugated Aldehydes, Ketones, Acids, Esters and Nitriles... 

Reduction of Conjugated Aldehydes In Preference to Nonconjugated Aldehydes... 

Selective reduction of aldehydes-1 Conjugated aldehydes are selectively reduced in the presence of nonconjugated ones by ErCl3 in aqueous ethanol. The effect is probably a result of preferential hydration of nonconjugated aldehydes. 

Scheme 11.4 Catalytic reduction of conjugated aldehydes with ethyl Flantzsch ester [12].

Asymmetric Organocatalytic Reduction of Olefins 395 Table 11.1 Organocatalytic reduction of conjugated aldehydes by Hantzsch ester 4 [14]. 

Selective reduction of ketones. Luche and Gemal have reported selective reduction of ketones in the presence of aliphatic aldehydes using sodium boro-hydride in combination with cerium(III) chloride. This reagent also effects selective reduction of conjugated aldehydes in the presence of saturated ones. 

DISSOLVING METAL REDUCTION AND RELATED REACTIONS OF NONCONJUGATED AND CONJUGATED ALDEHYDES AND KETONES... 

Tin Hydrides. Tributyltin hydride reduces aldehydes to primary alcohols by simply heating in methanol. °° A mixture of BusSnH and phenylboronic acid (p. 815) reduces aldehydes in dichloromethane. °° Reduction of ketones was achieved with Bu2SnH2 and a palladium catalyst. ° Using triaryltin hydrides with Bp3 OEt2, where aryl is 2,6-diphenylbenzyl, selective reduction of aliphatic aldehydes in the presence of a conjugated aldehyde was achieved. 

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