Steric influence of N-phosphorus-arylimines on the rhodium-catalyzed asymmetric arylation

Examination of the rhodium-catalyzed asymmetric arylation of benzaldehyde-imines bearing ethoxy, isopropoxy, phenyl, cyclohexyl, 3,5-xylyl, and 2,4,6-mesityl N-phosphorus activating/protecting groups revealed that bulky N-phosphorus groups retarded the arylation and at the same time prevented the competitive hydrolysis of an imine. Although the level of enantioselectivity was dependent favorably on the bulkiness ranging from 88% ee to 53% ee, the reactivity was drastically decreased along with bulkiness ranging from 95% to 3%.