Synthesis of 2-alkyl-2-boryl-substituted-tetrahydrofurans via copper(i)-catalysed borylative cyclization of aliphatic ketones.

A new method was developed for synthesizing 2-alkyl-2-boryl-tetrahydrofuran derivatives from aliphatic ketones using a copper(i)/N-heterocyclic carbene complex catalyst. This reaction presumably proceeds through the nucleophilic addition of a borylcopper(i) intermediate to ketone, followed by intramolecular substitution of the resulting alkoxide for the halide leaving group. The new borylation products, 2-alkyl-2-boryl-tetrahydrofuran derivatives with a condensed structure around the C-B bond, cannot be synthesized by other methods.

Copper(I)-Catalyzed Enantioselective Nucleophilic Borylation of Aliphatic Ketones: Synthesis of Enantioenriched Chiral Tertiary α-Hydroxyboronates.

A new method was developed for the first catalytic enantioselective borylation of aliphatic ketones. A variety of substrates reacted efficiently with bis(pinacolato)diboron in the presence of a copper(I)/chiral N-heterocyclic carbene complex catalyst to furnish optically active tertiary α-hydroxyboronates with moderate to high enantioselectivities (up to 94 % ee). Notably, the product could be converted into the chiral tertiary alcohol derivative using a stereospecific boron functionalization process. The theoretical study of the mechanism for the enantioselectivity is also described.