Synthesis of Potassium 5‐Bromopentyltrifluoroborate via Hydroboration of a Haloalkene

Abstract

Abstract This chapter presents the procedure for synthesis of potassium 5‐bromopentyltrifluoroborate via hydroboration of a haloalkene. While investigating nucleophilic substitution reactions involving boron‐containing electrophiles as a method to synthesize new pharmaceutical agents, the authors found boron's vacant p‐orbital caused problems in their syntheses. To overcome these difficulties, trifluoroborate salt electrophiles were explored as a method to mask the vacant p‐orbital. In conclusion, the authors have developed and reported a convenient, sequential synthesis as a general method for the preparation of potassium haloalkyltrifluoroborate salts through hydroboration with dichloroborane followed by treatment of the crude hydroboration products with potassium hydrogen difluoride. The reported procedure provided high yields and easy separation from disiloxane, a rarely mentioned hydroboration byproduct. This technique improves upon those that have been reported in terms of yield, reproducibility, atom economy, convenience, and cost for the generation of a series of potassium haloalkyltrifluoroborate salts.