Rearrangement Chemistry Forges Important Biaryl Motifs In Catalysts, Materials, Drugs

Biaryl motifs are so widespread—in antibiotics, in liquid crystals, and as ligands for asymmetric catalysis—that chemists value any new route to them. Obtaining enantiomerically pure biaryls has traditionally required multiple steps or inefficient resolutions. Now, László Kürti of the University of Texas Southwestern Medical Center and colleagues have developed sigmatropic rearrangement chemistry that circumvents those challenges. Instead of attempting to couple aryl rings directly, Kürti’s methods first involve forming a weak bond, such as N–N or N–O, and then performing a rearrangement to forge the strong aryl C–C bond. Neither method requires transition-metal catalysts, Kürti notes. One route (shown) harnesses a chiral phosphoric acid catalyst to impart chirality to the resulting biaryl (J. Am. Chem. Soc. 2013, DOI: 10.1021/ja401709k). The other adapts the mechanism of a 1990s-era indole synthesis to make the biaryls (J. Am. Chem. Soc. 2013, DOI:10.1021/ja400897u). To maximize the chiral selectivity of each process, Kürti’s team relied on computer models from Daniel H. Ess of Brigham Young University. “Both studies provide a new twist on a classic reaction,” says organic chemist Vy M. Dong of the University of California, Irvine. For obtaining tough-to-make diamino binaphthalenes, she adds, “I can’t think of a better protocol.”