Triorganoaluminum reagents

In addition to the above-mentioned aluminum halides (Section 6.5.3.1), triorganoaluminum reagents are also able to initiate cyclooligomerization processes of the phosphaalkyne 9 a. In these reactions, aluminum is incorporated directly into the cage system. The element combination phosphorus, carbon, aluminum in a polycyclic system was previously unknown. The product palette is highly influenced by the choice of the solvent and the substituents at the metal center. 

This chapter covers the recent literature reports (ca. 2003 onward) on asymmetric conjugate addition of triorganoaluminum reagents to enones, a,(3-unsaturated systems, nitroalkenes and also mechanistically closely related allylic alkylation of allylic phosphonates. It also includes cascade processes where the intermediate enolates (conjugate addition) and alkenes (allylic alkylation) are used for the synthesis of more complex molecules. This chapter is organized as follows. In Sect. 2 we present the results in the asymmetric conjugate addition. In this part, the... 

Other Michael acceptors have also been tested in the enantioselective conjugate addition of triorganoaluminum reagents. These mainly include activated substrates such as nitro-olefins and nitro-acrylates, 1,1 -dicarbonyl enones and... 

Triorganoaluminums with unsaturated C—C bonds adjacent to AI can be prepared from the respective organolithium, -sodium or -magnesium halide reagents. However, the solvate-free compounds (R = alkenyl, alkynyl) are unstable and, therefore, should be isolated as ether adducts ... 

When sterically more demanding trialkylaluminum reagents (R = i-butyl or 2-phenyl-propyl) are allowed to react with 9 a in diethyl ether or n-hexane, the cyclooligomerization process ends at the 1 3 compounds 82 (Scheme 6-21) [65J. The compounds have the structure of a triphosphametallahomobenzvalene, as has been confirmed for the case of R = CH2—CHPh —CH3 by X-ray crystallography. A plausible mechanistic rationale for the product formation involves a two-fold 1,2-addition of the triorganoaluminum to two equivalents of phosphaalkyne 9a (- 84). This is followed by a crossed [2 + 2]-cycloaddition... 

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