Diamine as Protecting Group for Iterative Suzuki-Miyaura Couplings

Suginome and co-workers report a convenient strategy for masking/unmasking boronic acids using 1,8-diaminonaphthalene. They hypothesized that the diamine will lower the Lewis acidity (and reactivity) of the boron. The protecting group is installed by refluxing in toluene with azeotropic removal of water. Remarkably, the masked boronyl group is stable to column chromatography. The original boronic acid can be recovered by stirring with dilute acid after the desired Suzuki-Miyaura cross-coupling reaction. Overall, this procedure was incorporated into efficient, iterative syntheses of oligoarenes. Further oligoarene functionalization was demonstrated via various known synthetic transformations (e.g., hydrogen peroxide oxidation and cross-coupling with alkenyl halides).