Dedicated to Professor Donald Matteson in recognition of his seminal contributions
to organoboron chemistry.
The use of an air-stable cationic hemiboronic acid catalyst for the chemoselective
reduction of enones is described. By changing the identity and stoichiometry of the
silane reducing agent, either the conjugate reduction products or the fully reduced
products can be obtained in high selectivity. In contrast to analogous reactions catalyzed
by air- and moisture-sensitive borane catalysts, the hemiboronic acid catalyzed protocol
can be performed under ambient conditions. Profiling studies revealed that global
reduction proceeds via a rapid initial 1,4-addition, followed by ketone deoxygenation
with a rate that is highly silane-dependent.
Key words
boronic acid catalysis - hemiboronic acids - reduction - deoxygenation - silanes