Enantioconvergent Synthesis of Tertiary Cyclic Allylboronates
Ge, Yicen; Cui, Xi-Yang; Tan, Siu Min; Jiang, Huan; Ren, Jingyun; Lee, Nicholas; Lee, Richmond; Tan, Choon-Hong
Angewandte Chemie, International Edition, 2019, 58, 2382-2386
Abstract: An enantioconvergent synthesis of chiral cyclic allylboronates from racemic allylic bromides was achieved by usinga guanidine-copper catalyst. The allylboronates were obtained with high γ/α regioselectivities (up to 99:1) and enantioselectivities (up to 99 % ee), and could be further transformed into diverse functionalized allylic compounds without erosion of optical purity. Exptl. and DFT mechanistic studies support an SN2' borylation process catalyzed by a monodentate guanidine-copper(I) complex that proceeds through a special direct enantioconvergent transformation mechanism.
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