A Solvent-Free Catalyst-Free Rapid Hydroboration of Ketones for a Green Synthesis of Secondary Alcohols

Solvent-free catalyst-free (“SFCF”) reactions have become of increasingly high interest due to their economic and operational advantages that coincide with their environmental favorability. Although several solvent-free methods have been recently described for the hydroboration of ketones using pinacolborane, many of them require catalysts, additives, or elevated temperatures to obtain high yields of the product alcohols within a reasonable timeframe. Herein, we report the first room temperature SFCF methodology utilizing the mild and stable reductant borane–ammonia for the hydroboration of ketones, providing the corresponding alcohols in up to quantitative yields after simple aqueous workup. This procedure has favorable green chemistry metrics and is highly scalable, safe, and more rapid than catalyzed alternatives. The rate can be easily controlled by the addition of trace amounts of water. Moreover, we have described a process for the swift cleavage of borate esters using the industrial byproduct hexafluorosilicic acid (H2SiF6), providing a potential application for an environmentally unfriendly waste.