Conjugate reduction-allylic

In 2013, Riant et al. developed a novel enantioselective domino conjugate reduction-allylic allylation reaction based on a cooperative dual catalysis involving a chiral copper catalyst and an achiral palladium catalyst. The reaction occurred between cyclic a-substituted a,(3-unsaturated ketones and ally methylcarbonate, providing the corresponding chiral cyclic a-allylic... 

Scheme 3.3 Domino conjugate reduction-allylic alkylation reaction catalysed by a combination of copper catalysis and chiral palladium catalysis.

The classification is unaffected by allylic, vinylic, or acetylenic unsaturation appearing in both starting material and product, or by increases or decreases in the length of carbon chains for example, the reactions f-BuOH f-BuCOOH, PhCHgOH - PhCOOH, and PhCH=CHCH20H -PhCH=CHCOOH would all be considered as preparations of carboxylic acids from alcohols. Conjugate reduction and alkylation of unsaturated... 

As allylic alcohols are unaffected by use of this catalyst it is proposed that the complete reduction occurs through competitive conjugate reduction, followed by subsequent reduction of the carbonyl. Although this catalyst is slower in action and results in low turnover numbers compared to some catalysts, it is inexpensive and provides good selectivity at room temperature. 

Conjugate reductions. This combination (usually 1 3 ratio) effects conjugate reduction of a,p-acetylenic ketones or esters to a, 3-enones or unsaturated esters at -50° with moderate (E)-selectivity. The HMPT is believed to function as a ligand to aluminum and thus to promote hydroalumination to give a vinylaluminum intermediate, which can be trapped by an allylic bromide (equation I).1 The re-... 

Conjugate reduction. Silicon hydrides and a Pd(0) catalyst reductively cleave allylic acetates selectively (equation I).1... 

Reduction of a,fi-unsaturated epoxides. Allylic alcohols can be prepared by-reduction of a,/3-unsaturated epoxides. Although yields are only moderate (40-h.S"/o), the method is stereoselective in that the (Z)-isomer is formed. The reaction is believed to involve conjugate reduction. ... 

Catalytic hydrogenation of an enone would not be chemoselective if an isolated double bond were also present in the molecule. However, isolated double bonds are inert to dissolving metal reduction. On the other hand, a variety of functional groups are reduced with alkali metals in liquid ammonia. These include alkynes, conjugated dienes, allylic, or benzylic halides and ethers. 

AIH3 reduces a,p-unsaturated amides to allylic amines [BK5] (Figure 3.87). a,p-Unsaturated amides and related compounds such as 3.224 are reduced to saturated amides by Li or K(5-Bu)3BH [Gl, GL7]. Trapping by alkyl halides has been described in many cases, such as 3.225 [KS1 ] (Figure 3.87). Conjugate reduction of... 

The various possibilities for the preparation of chiral allylic amines or a aryl substituted amines are outlined in Figure 1.9. Although the addition reaction of a carbon nucleophile to an imine derived from an aryl substituted aldehyde is very efficient (B), the related addition to an a,p unsaturated imine (A) can sometimes proceed via a 1,4 addition pathway. Similarly, the asymmetric C=N reduction reaction (C and D) is sometimes hampered by the possibility of either obtaining conjugate reduction (in the case of C) or low enantioselectivities (in D when R = aryl). The addition of sp hybridized carbanions to imines (E) is a particularly effective... 

Conjugate reduction. The double and tertiary amides are reduced b Dibal Debenzylation. Perbenzylated c>i debenzylated by Dibal-H in toluene in a debenzylated or AD-di-0,0-deben/> late Claisen rearrangement. Dibal-H rearrangement. Thus, allyl 4-r-but Iphcn at room temperature in 87% yield. b<0... 

Allylic alcohols. The tendency of NaBH4 to effect conjugate reduction of a,/3-unsaturated compounds is greatly reduced by C6F5OH. With borane scavenged by TMEDA or 1-hexene the selectivity is further improved. Only highly reactive ketones and acid chlorides are reduced by this reagent. ... 

House pointed out that 16 can disproportionate (as mentioned above) or that another mechanism may be operative in this reduction.24 Inverse addition of the hydride (a slurry of LiAlH4 is added to the carbonyl compound), short reaction times, and low reaction temperatures generally give moderate to good yields of the conjugate reduction product.24 Good yields of allylic alcohols can often be obtained from a,P-unsaturated aldehydes, however, when the reaction is done at low temperatures with strict control of the stoichiometry. 

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