Synthesis of Highly Substituted Oxaboroles from Oxaboranes via a Selective Petasis Borono-Mannich Reaction.

We present a novel and efficient method for the synthesis of highly substituted non-benzofused oxaboroles. Reactions of oxaboranes, morpholine, and salicylaldehyde in toluene heated to 85 °C for 4 h produce the corresponding oxaborole products in yields up to 93%. The process is effective across a diverse substrate scope and can be scaled to produce gram quantities of densely functionalized oxaboroles in excellent yield. Exclusive aryl transfer over vinyl transfer is observed. Computational insights further elucidate the inherent selectivity of this process.