Abstract
Aluminum organyls are valuable reagents for carbon-carbon bond formation as they can either be purchased at low prices or conveniently be prepared, for example, by hydro- or carboalumination of alkenes and alkynes. Although their application in reactions with α,β-unsaturated carbonyl compounds is rather limited, it creates a diverse picture concerning the selectivity of product formation which depends on several factors such as the type of organic residue, the conformation of the enone, the presence of additional functional groups and the donor ability of the solvent. This review describes issues of selectivity of such uncatalyzed transformations as well as conjugate additions catalyzed by achiral copper and nickel catalysts in which alanes can act similarly or even superiorly to the more common lithium or magnesium organyls. Moreover, the rapidly growing field of transition-metal-catalyzed asymmetric 1,2- and 1,4-additions is reviewed, in which aluminum reagents can not only lead to enantioselective alkyl additions, thus substituting zinc organyls, but also afford introduction of aryl, alkenyl and alkynyl groups.
1 Introduction
2 Uncatalyzed Additions to α,β-Unsaturated Carbonyl Compounds
2.1 Regioselectivity with Plain Enones
2.2 Selective Conjugate Additions to Cyclic Enones
2.3 Conjugate Additions to Carboxylic Compounds
3 Racemic Copper- and Nickel-Catalyzed 1,4-Additions
4 Asymmetric Addition to Carbonyl Compounds
4.1 Enantioselective Conjugate Additions to Enones
4.2 Enantioselective 1,2-Additions
5 Conclusion
Key words
aluminum - asymmetric catalysis - nucleophilic additions - organometallic reagents - regioselectivity
