Menthoxyaluminum dichloride

The chiral Lewis acid catalyzed cycloaddition of methacrolein 310 to cyclopentadiene predominantly affording exo cycloadduct 322 together with some 323 has been extensively investigated. The application of menthoxyaluminum dichloride (324) as the chiral catalyst in this reaction represents one of the earliest examples of a chiral Lewis acid catalyzed Diels-Alder reaction206 (equation 90). The authors confirmed their results in 1987, but the ee was revised from 72% to 57%207. 

Recently, Diels-Alder reactions between cyclopentadiene and menthoxyaluminum dichloride-acrolein complexes were investigated by means of combined AM1/AM3 calculations and the results were compared to full AMI results211. 

Enantiomer selection is also found in vinyl ether polymerization [226,227], The polymerization of cis- and trans- 1-methylpropyl propenyl ethers using (-)-menthoxyaluminum dichloride [227] and the copolymerization of rac- 1-methylpropyl vinyl ether with optically active monomers [226] are enantiomer selective. 

Menthoxyaluminum dichloride (1). Mol. wt. 253.15. This reagent is prepared by reaction of (-menthol and ethylaluminum dichloride in heptane at —78°. 

In 1979, Koga and coworkers disclosed the first practical example of a catalytic enantioselective Diels-Alder reaction [44] promoted by a Lewis acidic complex, presumed to be menthoxyaluminum dichloride (1), derived from menthol and ethylaluminum di chloride, whose structure remains undefined [45]. This complex catalyzed the cycloaddition of cyclopentadiene with acrolein, methyl acrylate, and methacrolein with enantioselectivities as high as 72% ee. Oxidation of 2 (predominantly exo) followed by recrystallization actually lowered the ee ... 

---