Enones reductive alkylation

As first demonstrated by Stork,the metal enolate formed by metal-ammoni reduction of a conjugated enone or a ketol acetate can be alkylated in liquic ammonia. The reductive alkylation reaction is synthetically useful since ii permits alkylation of a ketone at the a-position other than the one at whicf thermodynamically controlled enolate salt formation occurs. Direct methyl-ation of 5a-androstan-17-ol-3-one occurs at C-2 whereas reductive methyl-... 

ENONE REDUCTION-ENOLATE ALKYLATION SEQUENCE 2 - ALLYL- 3-METH YLC Y CLOHEX AN ONE... 

The present procedure utilizes the enone reduction-cnolate alkylation... 

The direct conversion of 3-methylcyclohex-2-enone into 2-allyl-3-methylcyclohexanone provides an interesting example of the utility of the reduction-alkylation procedure. Synthesis of this compound from 3-methy I cyclohexanone would be difficult because the latter is converted mainly into 2-alkyl-5-methylcyelohexanones either by direct base-catalyzed alkylation11 or by indirect methods such as alkylation of its enamine (see Note 13) or alkylation of the magnesium salt derived from its cyclohexylimine.12... 

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

Asymmetric reduction of a,fi-enon s. This combination of reagents (1 1) in conjunction with N-cthylaniline (2 equivalents) reduces alkyl aryl ketones to alcohols with high stereoselectivity.1 Under these conditions 2,/1-unsaturated ketones arc reduced to optically active (S)-allylic alcohols. Optical yields of 80 98% have been reported for open-chain enones. Reduction of cyclic enones is somewhat less efficient. The method was used to reduce 1 to 2, which has been used as an intermediate in an anthracyclinone synthesis.2... 

Reductive alkylation of a, -enones. This reaction can be effected by a photo-stimulated free-radical reaction with RHgCl and a base (K1/K2S208, Nal, DABCO).1... 

Regeneratable polymeric organotin dihydride beads have been used to reduce halides selectively (e.g. 3-bromocamphor to camphor).52 /3-Unsubstituted cyclohex-enones undergo exclusive and almost quantitative 1,4-reduction by potassium tri-s-butylborohydride to the corresponding saturated ketone [e.g. (16)] 53 reductive alkylation of carvone proceeds similarly to (17 R = Me, X = H).53 In contrast,... 

Friedel-Crafts reactions. The reaction of osmium-complexed anisoles with electrophiles such as enones is catalyzed by TfOH. Benzylation of arenes by a reductive alkylation with arenecarbaldehyde acetals involves an intramolecular redox process (hydride shift) after protonation of the benzylic ether intermediates. 

Reductive alkylation. Stork and Logusch1 have extended the reductive alkylation of a,/J-enones (3, 179-181) to enediones (equation I). One useful feature is... 

The intermediate enolates (a) can also be trapped by a reactive electrophile. In this case the enone is added to lithium tri-sec-butylborohydride in the absence of an alcohol, and the alkylating agent is added after 20 min. Products of this reductive alkylation are obtained in yields of 50-60%. 

Reductive alkylation of enones. Tin(IV) enolates are formed via the ketyls, which are derived from enones and BujSnH. Reaction of the enolates with aldehydes furnishes aldols. Quenching the enolates with alkyl halides in the presence of HMPA gives a-alkylated products. ... 

ENONE REDUCTION-ENOLATB ALKYLATION SEQUENCE 2-ALLYL-3-METHYLCYCLOHEXANONE... 

---