We are grateful for financial support from the Natural Sciences and Engineering Research Council (NSERC), the University of Toronto (U of T) and Alphora Research Inc. M.L. thanks the Canada Council for the Arts for a Killam Fellowship. A. Lough (U of T) is acknowledged for X-ray analysis. Z.S. is a visiting scholar from China Pharmaceutical University and thanks the China Scholarship Council. F.S. and T.S. thank the RWTH Aachen and the Evonik Foundation (scholarship to T.S.) for funding. Y.Y. thanks the Osaka University Scholarship for Overseas Research Activities 2015. C.K. is grateful for the award of a Synthesis and Solid State Pharmaceutical Centre PhD Scholarship. D. Schmidmeier is acknowledged for the synthesis of some substrates. We also thank T. Rovis (Columbia University) for suggestions on the mechanism of the reaction and providing chemicals and equipment during the revision of this manuscript, S. S. Stahl (University of Wisconsin-Madison), M. S. Taylor (U of T), D. A. Petrone (U of T), C. C. J. Loh (Max-Planck-Institut für Molekulare Physiologie, Abteilung Chemische Biologie) and I. A. Sanhueza (RWTH Aachen) for helpful discussions. M. Sickert (University of Leipzig) is acknowledged for his initial exploration in this area. This paper is dedicated to Professor Barry M. Trost on the occasion of his 75th birthday.