Novel binaphthyl and biphenyl α- and β-amino acids and esters: organocatalysis of asymmetric Diels–Alder reactions. A combined synthetic and computational study?

Organic & Biomolecular Chemistry Pub Date: 2018-09-17 DOI: 10.1039/C8OB01795F

Abstract

Asymmetric catalysis of the Diels–Alder reaction between cyclopentadiene and cinnamaldehydes has been studied using as catalysts a range of novel α- and β-aminoacids and aminoesters with binaphthyl and biphenyl backbones, providing enantioselectivities of up to 62% ee. B3LYP/6-31G* calculations, including free energy corrections, have been carried out on a binaphthyl catalyst example to identify transition state structures and to aid in the identification of major enantiomers. The calculated product ratios agree well with the experimental data; the transition states identified involve preferential approach of cyclopentene along a trajectory adjacent to the acid/ester group. The four lowest energy transition states display a stabilizing dipolar interaction between the carbonyl group oxygen atom and a terminal proton of the diene unit.

Graphical abstract: Novel binaphthyl and biphenyl α- and β-amino acids and esters: organocatalysis of asymmetric Diels–Alder reactions. A combined synthetic and computational study
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