Palladium-catalyzed borylation of l-tyrosine triflate derivative with pinacolborane: practical route to 4-borono-l-phenylalanine (l-BPA) derivatives

Efficient palladium-catalyzed borylation of protected l-tyrosine triflate with pinacolborane was achieved despite previous reports to the contrary. In addition to the use of an inexpensive boron source, the reaction was carried out in the presence of only 0.5 mol % palladium catalyst. Furthermore, the borylation can be performed using pinacolborane prepared in situ from pinacol and borane–diethylaniline complex. This represents a practical entry to 4-borono-l-phenylalanine (l-BPA) derivatives.