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Transition Metal-Free Trans Hydroboration of Alkynoic Acid Derivatives: Experimental and Theoretical Studies
Russell Fritzemeier1, Ashley Gates1, Xueying Guo2
1Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24061 , United States.
Abstract:
We report a phosphine-catalyzed trans hydroboration of alkynoate esters and amides. The reaction proceeds under mild conditions with exclusive ( E)-selectivity to afford ( E)-β-boryl acrylates and ( E)-β-boryl acrylamides in good to excellent yields. The reaction is tolerant of a variety of functional groups and allows efficient access to novel oxaboroles as well as a pargyline derivative (MAO inhibitor). Theoretical calculations suggest an internal hydride generates a phosphonium allenoxyborane followed by the formation of a key phosphonocyclobutene intermediate that collapses in a stereoselective, rate-limiting step.
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