Enantioselective Diels-Alder Using a Bimetallic Catalyst

Significance

A highly regio-, enantio- and dia­stereoselective Diels-Alder reaction of 2,4-hexadienol with methyl acrylate through use of a chiral bimetallic Lewis acid catalyst is reported. Mechanistic studies suggest that zinc coordinates to the dienol and to one alcohol group of BINOL, while magnesium coordinates to the acrylate and the other alcohol of BINOL; thus, the order of addition of reagents is important. The hypothesis of an ‘intramolecular type’ mechanism was supported by competition experiments which showed that the yield of the desired product was unaffected by concentration, whereas the competing reaction between cyclopentadiene and methyl acrylate was more efficient at higher concentrations.