Unsaturated aryllithiums

The sesquiterpenoid hydrocarbons (5)-a-curcumene (59) and (5)-xanthorrhizol (60) were prepared by asymmetric conjugate addition of the appropriate aryllithium reagent to unsaturated oxazoline 56 to afford alcohols 57 (66% yield, 96% ee) and 58 (57% yield, 96% ee) upon hydrolysis and reduction. The chiral alcohols were subsequently converted to the desired natural products. ... 

Alkyl and aryllithium compounds have been found to undergo 1,4-addition with the salts of a, (3-unsaturated acids.328 This result reflects the much reduced reactivity of the carboxylate carbonyl group as an electrophile. 

Xu and co-workers performed similar transformations on cr,/3-unsaturated tert-butyl esters 5 with aryllithium reagents. The use of functionalized substrates and aryllithiums is the key feature of this study (Scheme 3).6... 

Chiral /3,/3-diaryIpropionic acid moieties are often found in compounds showing biological activities, such as antiarrhythmics vasodilators antidepressives " , antihistamines and controllers of cerebral insufficiency ". In the course of synthetic studies of chiral -diaryIpropionic acid derivatives, Merck researchers developed stereoselective conjugate addition of aryllithium reagents to the a,/ -unsaturated fert-butyl esters 18 bearing a chiral imidazolidine or oxazolidine auxiliary at the ortho position of an aryl group. The addition furnished chiral -diaryIpropionic acid derivatives 19 with... 

The range of carbon nucleophiles that have been successfully employed for 1,4-addition to -a,/i-unsaturated iron-acyl complexes is limited to simple alkyl- and aryllithium species. Grignard reagents and the 1,3-propanedioate anion are reported to fail to react with. E-complexes36. The effect of varying the phosphane ligand has been examined little effect upon... 

Similarly, organolithiums (or Grignard reagents) add to ester (26) to afford silyl enolates which are intercepted with aldehydes and ketones to give a,p-unsaturated esters (27),434 while addition of the bifunctional aryllithium (28) (MIRC protocol) affords the 2-(trimethylsilyl)tetrahydronaphthoate ester (29 Scheme 7).43b... 

Although alkyl- and aryllithium reagents usually attack the carbonyl group of a, j3-unsaturated carbonyl compounds (1, 2-addition), conjugate addition (1, 4-addition) is observed with very hindered esters where approach to the carbonyl group is impeded, as in 2,6-di-terr-butyl-4-methylphenyl esters (butylated hydroxytoluene, BHT esters) and 2,6-di-tert-butyl-4-methoxyphenyl esters (butylated hydroxyanisole BHA esters). ... 

An interesting development in asymmetric additions to azomethines employs chiral ligands (chelating agents) on the organometallic. Tomioka has shown that the same ligand used for addition of aryllithiums to unsaturated esters cf. Scheme 4.10) also works for unsaturated imines, as illustrated in Scheme 4.15 [154]. The... 

A p-aryl-a,p-unsaturated ferf-butyl ester 7 bearing a chiral imidazolidine (or oxazolidine) auxiliary at an ortho position undergoes stereoselective conjugate addition of an aryllithium reagent 8, furnishing a p,p-diarylpropionic acid derivative 9 in up to 97% ee (Scheme 3) [17],... 

Xu, E. Tillyer, R.D. Tschaen, D.M. Crabowski, E.J.J. Reider. P.J. Enantioselective 1.4-addition of aryllithium reagents to a,p-unsaturated tert-butyl esters in the presence of chiral additives. Tetrahedron Asymmetry 1998. 9. 1651-1655. 

Similarly, addition of alkyl, vinyl, or aryllithiums to a-halo-a,(3-unsaturated acylsilanes generates a-silyl alkoxide 19, which can collapse to give allenol silyl ethers 20 (Scheme 6T3).27... 

Scheme 13). D-Glucose furnished an unsaturated nitro-sugar which underwent Michael addition with an aryllithium reagent to yield the intermediate (61), leading on to (+)-lycoricidine (62)(Scheme 14). ... 

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