Enones conjugate reduction

The key step in a short and efficient synthesis of pleraplysillin-1 (127) is the palladium-catalyzed cross-coupling of vinylstannane 125 with vinyl triflate 126 (see Scheme 33). This synthesis is noteworthy in two respects. First, vinyl triflate 126 is generated regio-specifically from the kinetic enolate arising from a conjugate reduction of enone 124 the conjugate reduction of an enone is, in fact, a... 

This section contains alkylations of ketones and protected ketones, ketone transpositions and annulations, ring expansions and ring openings and dimerizations. Conjugate reductions and Michael alkylations of enone are listed in Section 74 (Alkyls from Alkenes). 

Conjugate reductions and reductive alkylations of enones are listed in Section 74 (Alkyls from Alkenes). 

Copper hydride species, notably Stryker s reagent [Ph3PCuH]6, are capable of promoting the conjugate reduction of a,( >-unsalurated carbonyl compounds [42], Taking advantage of this trustworthy method, Chiu et al. demonstrated in 1998 an intramolecular reductive aldol reaction in the synthesis of novel terpenoid pseudolaric acids isolated from Chinese folk medicine (Scheme 28) [43]. Two equivalents of [Ph3PCuH]6 enabled cycli-zation of keto-enone 104 to provide the bicyclic diastereomers 105 (66%) and 106 (16%). The reaction also was applied to the transformation of 107... 

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 hydrogenation. The combination of zinc and NiCl2 (9 1) effects conjugate reduction of a,(3-enones in an aqueous alcohol in which both the enone and product are completely soluble. Ultrasound increases the rate and the yields. Presumably the salt is reduced to a low-valent form that is absorbed on the zinc. No reduction takes place with a 1 1 Zn-NiCl2 couple. The method is not applicable to a,(3-unsaturated enals. Isolated double bonds are also reduced by this method, but this hydrogenation can be inhibited by addition of ammonia or triethylamine. 

Copper-mediated conjugate reductions of enones and enoates were reported in 1988 by Stryker and co-workers (188). Stryker and Mahoney (189) showed that the reaction could be made catalytic in copper under an atmosphere of hydrogen gas however, under these conditions, overreduction was observed. In 1998, Lipshutz... 

Conjugate addition to 1 proceeded across the open face of the bicyclic system to give an enolate, condensation of which with the enantiomerically-pure aldehyde 8 gave the enone 9. Conjugate reduction of the enone also removed the benzyl ether, to give the alcohol. Conversion of the alcohol to the azide gave 10. Ozonolysis followed by selective reduction then gave 2. 

Conjugate reduction of enones. a./ -Unsaturated ketones and aldehydes undergo 1,4-reduction in generally high yield with I equivalent of lithium aluminum hydride in the presence of 10 mole % of Cul and 1 equivalent of HMPT at -78°. The active agent presumably is LiHCuI. Cul can be replaced by mesitylcoppcr and copper(I) t-butoxide. 

This system when catalyzed by ZnCl2 can effect conjugate reduction of a,p-enones and -enals.2... 

Stereoselective acyclic enolization2 This reaction can sometimes be achieved by conjugate reduction of acyclic a,(3-enones by lithium tri-sec-butylborohydride (1). When an enone reacts with 1 mainly by 1,2-reduction Li/NH3 can be used for conjugate reduction. In at least one case reduction with 1 is more stereoselective than that with Li/NH3. The stereoselectivity in general can be correlated with conformational preferences of enones.3... 

Enol triflatesfrom affi-enones.1 The reaction can be carried out by conjugate reduction of the enone with lithium tri-sec-butylborohydride followed by reaction of the resulting enolate with N-phenyltriflimide. The method is generally useful, but 1,2-reduction can predominate in the case of (3,(3- or even y,y-disubstituted a,(3-enones. 

Conjugate reduction of enones.1 Under phase-transfer conditions (Aliquat, NaHC03), a,0-enones undergo exclusive 1,4-reduction with Na2S204 (yields 70-85%). 

Conjugate reduction of a,/l-enals and -enones. Tri-n-butyltin hydride in the presence of tetrakis(triphenylphosphine)palladium effects conjugate reduction of a, /J-unsaturated aldehydes and ketones in the presence of a proton source (water, acetic acid). Yields are improved by addition of a radical scavenger.15 Double bonds bearing... 

Conjugate reductions of a,(l-enones.2 a., fi-Enones react with triisobutylaluminum in pentane solution to give products of 1, 2-addition and 1, 2-reduction. The former... 

Conjugate reduction of tt,fi-enones. Lithium bronze can be used in place of lithium blue for conjugate reduction of cyclic a,(3-enones to the saturated ketone in high yield it requires an added proton source ((-butyl alcohol). 

---