Synthesis of Fluorinated Aminoalkylboronic Acids from Amphoteric α‐Boryl Aldehydes

Our ongoing search for underdeveloped functional group combinations has brought to light α‐fluorinated aminoalkylboronic acids, a new class of molecules featuring the B‐CF linkage. These compounds can now be generated from secondary amines and α‐boryl aldehydes through electrophilic fluorination of boryl enamines or enamides. Fluorinated β‐aminoalkylboronic acids show no signs of degradation under ambient conditions. We present evidence for the involvement of chair‐like motifs, favored over the acyclic forms by up to 1.7±0.1 kcal mol −1 in water and held together by an amine‐boronate hydrogen bond. Fluorinated β‐aminoalkylboronic acids are stable over a wide pH range and are characterized by a p K a of 3.4, which is the lowest of any alkylboronic acid.