Organoaluminum reagents conjugate additions

Organoaluminum reagents are inexpensive and readily available in large quantities. However, only a few examples of conjugate additions using trialkylaluminum nucleophiles have been reported. 

The asymmetric synthesis of / -branched carboxylic acid derivatives was accomplished by conjugate addition of mixed organoaluminum reagents to optically active Arabinose-derived c -unsaturated A-acyloxazolidinones (Scheme 47). Efficient stereocontrol was achieved using different optically active bicyclic oxazolidinones, yielding (.R)- or ( -configured / -branched carboxylic acid derivatives.136a... 

Organoaluminum reagents have been used in the copper-catalyzed conjugate addition to enones with some success. Iwata and co-workers (182) demonstrated that dimethoxyphenyl oxazoline (247) provides modest selectivities in the copper-catalyzed conjugate addition of trimethylaluminum to 3,4,4-trimethylcyclohexadi-enone to provide the adduct in 68% ee, Eq. 145. The use of TBSOTf is crucial to attain high conversion and selectivity in this process. Woodward and co-workers (183) subsequently reported that a Cu(I) complex of thiocarbamate 248 provides modest facial discrimination in the addition of trimethylaluminum to a linear enone to afford 245b in 51% ee, Eq. 146. The authors note that this catalyst system decomposes under the reaction conditions at ambient temperature. 

Enantioselective conjugate addition to construct a cyclic quaternary center has been a particular challenge. Alexandre Alexakis has also shown (Angew. Chem. Int. Ed. 2005,44, 1376), as illustrated by the conversion of 9 to 13, that Cu -catalyzed organoaluminum reagents work effectively in this context. 

The conjugate addition of organoaluminum reagents to quinols is directed by the hydroxy group at C-4. ... 

Alkynylation of enones. The nickel catalyst obtained from Ni(acac)2 and DIBAH catalyzes the conjugate addition of organoaluminum acetylides even to transoid enones. The acetylenic aluminum reagent is prepared according to Fried s procedure (4, 144) from a lithium acetylide and dimethylaluminum chloride. In all cases only 1,4-addition is observed. -Examples ... 

Stereoselective conjugate addition of organoaluminum reagents has been performed by employing a, (3-unsaturated carbonyl compounds having chiral auxiliary. Kunz et al. have demonstrated the asymmetric 1,4-addition of a,(3-unsaturated... 

Elzner S, Maas S, Engel S, Kunz H (2004) Stereoselective conjugate addition of mixed organoaluminum reagents to a,P-unsaturated Al-acyloxazolidinones derived liom carbohydrates. Synthesis 2153-2164, and references cited therein... 

Carreno MC, Gonzalez MP, Ribagorda M (1998) Studies of diastereoselectivity in conjugate addition of organoaluminum reagents to (/f)-[(p-Tolylsulfinyl)methyl]quinols and derivatives. J Org Chem 63 3687-3693... 

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