Abstract

Hydroboration of simple ketones and alkynes are well-established transformations in organic synthesis. However, hydroboration of ynones, a family of electron-poor alkynes containing carbonyl-conjugated C≡C bonds, has been less explored. Currently the modes of reactivity only follow simple ketones and alkynes, and there is limited progress in developing new reaction modes of ynones. In this context, we discovered a ruthenium-catalyzed hydroboration of ynones with unusual selectivity, leading to structurally novel and synthetically useful but previously inaccessible products, vinyl α-hydroxylboronates.1 It features high efficiency, mild conditions and complete chemo-, regio-, and stereoselectivity, Both control experiments and DFT calculations indicated a nontraditional two-step mechanism involving initial rate-determining 1,4-conjugate addition of hydroborane to form the key boryl allenolate intermediate followed by a fast second hydroboration of the enolate motif of the allenolate. A thorough and systematical computational study gave a reasonable understanding of the unusual reactivity and intrinsic origin of selectivity. 

Reference：

1. Feng, Q.; Li, S.; Li, Z.; Yan, Q.; Lin, X.; Song, L.; Zhang, X.; Wu, Y.-D.; Sun, J. J. Am. Chem. Soc. 2022, 144, 14846.