Highly Lewis Acidic In Situ‐Generated Boronic Acid Ester: A Practical Catalyst for Hosomi–Sakurai Conjugate Addition, Carbonyl‐Ene Reaction, and Silane‐Mediated Amide Reduction

Lewis acids are electron‐pair acceptors that form adducts with Lewis bases. These compounds have attained a prominent position in chemistry, finding widespread utility in diverse applications like catalysis and materials science. In this context, boron Lewis acids have become increasingly indispensable in organic synthesis due to their strong electrophilic nature, which renders them useful catalysts across a variety of chemical transformations, including C–C bond formations and C–H bond functionalization. This work details the catalytic efficacy of a newly developed in situ‐generated boronic acid ester (BAE) Lewis acid system in promoting conjugate addition of allylsilanes, carbonyl‐ene reactions and amide reductions. Notably, the Lewis acidity of this catalyst is demonstrated to be comparable to that of tris(pentafluorophenyl)borane and surpassing prior BAE catalysts from our laboratory .