Enantioenriched Allylesters via a Copper-Catalyzed Diene Carboesterification with Alkyltrifluoroborates and Carboxylic Acids

The rapid synthesis of a range of enantioenriched allylic esters is enabled by a new 3-component catalytic enantioselective 1,2-carboesterification of readily available dienes with carboxylic acids and potassium alkyltrifluoroborates. The chiral copper catalyst, formed in situ from Cu(OTf)₂ and (4S,4′S)-2,2′-(cyclopentane-1,1-diyl)bis(4-phenyl-4,5-dihydrooxazole), is implicated in both the generation of alkyl radicals from the alkyltrifluoroborates as well as the enantioselective formation of C-O bonds. Potassium salts of primary and secondary alkyltrifluoroborates as well as several benzylic trifluoroborates, tert-butyltrifluoroborate, and phenyltrifluoroborate participate in the reaction. The regioselectivity and enantioselectivity are strongly impacted by variations in all of the reaction components, which in turn are thought to impact the C-O bond-forming reductive elimination from a [Cu(III)] intermediate.