VAPOL-aluminum catalyst

The observations made for the VAPOL-aluminum catalyst in Table 15 are suggestive of asymmetric auto-induction similar to that for catalysis of the same reaction by a chiral aluminum catalyst prepared from the diol 225 (Sch. 24 Fig. 1) [48]. Because the Diels-Alder reaction between methacrolein and cyclopentadiene was too fast, monitoring of the time course of asymmetric induction, thus this was done for the reaction between methyl acrylate and cyclopentadiene [53]. The VAPOL-aluminum catalyst catalyzes the reaction of methyl acrylate and cyclopentadiene with asymmetric auto-induction as indicated in Fig. 2. The first data point that was collected was after 20 % conversion, at which point the cycloadduct 141 was 47 % ee when the last data point was collected at the end of the reaction it was found that 141 was 82 % ee. 

Wulff and coworkers have applied their aluminum catalyst 2 containing a vaulted biphenanthrol ligand (VAPOL, Section 2.1) to the Diels-Alder reaction between methyl acrylate and cyclopentadiene [25] (Scheme 1.32). In this Diels-Alder reaction auto-induction is observed, because of a cooperative interaction between the product... 

In a similar [4+2] reaction of a, -unsaturated esters, the aluminum catalyst complexed with the ligand S-VAPOL resulted in autoinduction , because of cooperative interaction of the product with the catalyst to generate a more selective catalytic species (Scheme 6.48) [68]. The ee% gradually increased as the reaction time lengthened. In the proposed intermediate, penta-coordinated aluminum complex 77, the cycloadduct is recognized as a complementary ligand, leading to substantial asymmetric induction. The acrylate is activated effectively within this hybridized complex which adopts pentacoordination [87]. 

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