Dienolates alkylation, stereochemistry

The stereochemistry of alkylations of extended dienolates of enones such as (70) has been extensively investigated (Scheme 33).In general, the results are similar to those found for the related decalone enolates (43a) and (44), i.e. steric factors within the anion play a dominant role. Thus, axial attack is preferred with (70 R = H), but equatorial attack is strongly favored when an angular methyl group is present (70 R = Me). There is a modest preference for axial alkylation when an angular ethoxycarbonyl... 

Alkylation of the dienolate ion derived from 4-methyl-19-nortestosterone (313) with CD3I in benzene solution gave the 4,4-dimethyl compound (314), with 70% of the labelled methyl groups in the 4j5-orientation. With t-butyl alcohol as solvent the product showed predominant (90%) introduction of 4a-CD3 (iWs latter conclusion, which reverses that reached in an earlier study, depended upon application of the nuclear Overhauser effect for the assignment of n.m.r. signals of the C-4 methyl groups). Solvent-dependence of the stereochemistry of alkylation has not been suspected before. ... 

The dienolate anion of 190 generated with potassium r-amyloxide was alkylated with 191 to yield the mixture 192 (R = OCH2CH2O) in 54% yield. Acid-catalyzed hydrolysis gave the crystalline mixture of ketones. The stereochemistry at C-1 was assigned on the basis of previous observation,and the benzene induced shifts of methyl signals in the nmr spectrum, confirmed by the X-ray structure determination. 

Kende AS, Toder BH (1982) Stereochemistry of Deconjugative Alkylation of Est Dienolates. Stereospecific Total Symthesis of the Litsenolides. J Org Chem 47 163... 

Kende, A. S. and Toder, B. H., Stereochemistry of deconjugative alkylation of ester dienolates stereospecific total synthesis of the htsenoHdes, /. Org. Chem., 47,167,1982. 

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