Copper-catalyzed synthesis of allenylboronic acids. Access to sterically encumbered homopropargylic alcohols and amines by propargylborationElectronic supplementary information (ESI) available: Detailed experimental procedures and compound characterization data are given. CCDC 1550097. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc05123a

Tri- and tetrasubstituted allenylboronic acids were prepared via a new versatile copper-catalyzed methodology. The densely functionalized allenylboronic acids readily undergo propargylboration reactions with ketones and imines without any additives. Catalytic asymmetric propargylborylation of ketones is demonstrated with high stereoselectivity allowing for the synthesis of highly enantioenriched tertiary homopropargyl alcohols. The reaction is suitable for kinetic resolution of racemic allenylboronic acids affording alkynes with adjacent quaternary stereocenters. Synthesis and application of allenylboronic acids is presented. The successful synthetic applications are based on the possibility of the versatile transformations of the unprotected B(OH) 2 group in situ under the propargylboration conditions.