Brook/Elimination/Aldol Reaction (BEAR) Sequence for the Direct Preparation of Fluorinated Aldols from β,β-Difluoro-α-(trimethylsilyl)alcohols

A methodology allowing the preparation of aldols featuring a fluorinated stereogenic center is reported. The corresponding fluoroenolates are formed in situ from stable beta,beta-difluoro-alpha-(trimethylsilyl)alcohols, through a base-mediated process involving a Brook rearrangement followed by a fluoride elimination, and are directly added to aromatic aldehydes. Two different sets of conditions were disclosed. The first one involves the stoichiometric addition of potassium tert-butoxide (t-BuOK) while the second is based on the use of a catalytic amount of an ammonium phenoxide. The latter opens the way for a catalytic and asymmetric version of this Brook/elimination/aldol reaction (BEAR) sequence.