Boronyl Borinic Esters: Preparation as B₂pin₂/^secBuLi/TFAA Adducts, Structural Insights and Reactivity in Pd‐catalyzed Allylic Borylation

Abstract

Novel boronyl borinic ester I was generated by quenching the B2pin2/secBuLi‐ate complex with trifluoroacetic acid anhydride (TFAA) via ring‐opening in the 1,3,2‐dioxaborolane moiety on ate‐boron. Detailed NMR studies of the B2pin2/secBuLi‐ate complex in solution and in solid state allowed us to assume its oligomeric nature in solids with only ate‐boron involved in the oligomerization process. The O‐trifluoroacetyl pinacolate residue on borinic ester I initially formed on quenching with TFAA undergoes an unusual intramolecular transesterification with the carbonyl group of trifluoroacetyl forming othroester moiety in a few hours at r. t. to give boronyl borinic ester II. A solution of these reagents I/II was proved to be efficient for borylation of (2‐fluoroallyl)pyridinium salts that are highly base sensitive.