July 6, 2017
A new method for constructing both symmetrical and unsymmetrical diaryl-, arylalkyl-,
and dialkylamines now gives chemists a general way to make these important molecular
motifs without having to use transition metals and ligands.
Umpolung—the fun-to-say chemical phenomenon in which a functional group's polarity is reversed—underlies the new method. Chemists, led by László Kürti of Rice University, Daniel H. Ess of Brigham Young University, and Guigen Li of Nanjing University and Texas Tech University, have come up with a series of imines and an oxime—all derived from malonate—in which normally nucleophilic nitrogen becomes an electrophile. The polarity inversion can be attributed to the electron-density-withdrawing power of some neighboring carbonyl groups on those molecules. That property, plus some bulky substituents, guide nucleophiles such as Grignard reagents to preferentially attack this unusually electrophilic nitrogen. A single attack on an imine can lead to unsymmetrical products, while a double attack on the oxime produces symmetrical ones (J. Am. Chem. Soc. 2017, DOI: 10.1021/jacs.7b05279).