Stoichiometric reductions of alkyl-substituted ketones and aldehydes to borinic esters.

A series of alkyl-substituted ketones are shown to activate hydrogen in the presence of B(C6F5)3, affording the corresponding borinic esters RR'CHOB(C6F5)2. The mechanism is shown to proceed via H2 activation, hydride delivery and protonation of a C6F5 group. The aliphatic aldehyde Et2CHCHO reacts with B(C6F5)3 or BPh3 to give boron enolates Et2C[double bond, length as m-dash]CH(OBAr2) (Ar = C6F5, Ph). These latter species are amenable to FLP-catalyzed reduction to the corresponding borinic esters.