Complexity-generating hydration reactions via gold-catalyzed addition of boronic acids to alkynes

Abstract

Boronic acids can serve as organic soluble substitutes for water molecules in the metal-catalyzed hydration of alkynes. The Au-catalyzed addition of boronic acids to alkynes provides an alternative method for enolate generation, which proceeds under exceptionally mild conditions. The resulting enolates can be trapped by aldehydes present in the reaction mixture, giving aldol products that can be isolated as cyclic borate esters. These compounds are versatile synthetic intermediates that can be elaborated into a variety of products by transformation of the boron moiety. The Au-catalyzed reaction of boronic acids with propargylic alcohols results in efficient Meyer–Schuster rearrangement to the corresponding enones. The rearrangement of tertiary alcohols gives (E)-enones with moderate to good selectivity, and the addition of a boronic acid to the reaction appears to enhance the level of geometrical control. The rearrangement of primary alcohols to terminal enones also occurs readily in the presence of catalytic Au(I) and a boronic acid, and the resulting terminal enones can be reacted with nucleophiles in one-pot procedures to give a variety of β-substituted ketones.