Stereoselectivity control in Rh-catalyzed β-OH elimination for chiral allene formation

Jie Wang; Wei-Feng Zheng; Xue Zhang; Hui Qian; Shengming Ma

doi:10.1038/s41467-023-42660-1

Stereoselectivity control in Rh-catalyzed β-OH elimination for chiral allene formation

Nat Commun. 2023 Nov 16;14(1):7399. doi: 10.1038/s41467-023-42660-1.

Authors

Jie Wang^#¹, Wei-Feng Zheng^#¹, Xue Zhang², Hui Qian³, Shengming Ma^{4

5}

Affiliations

¹ Research Center for Molecular Recognition and Synthesis, Department of Chemistry, Fudan University, Shanghai, 200433, PR China.
² State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai, 200032, PR China. xzhang@sioc.ac.cn.
³ Research Center for Molecular Recognition and Synthesis, Department of Chemistry, Fudan University, Shanghai, 200433, PR China. qian_hui@fudan.edu.cn.
⁴ Research Center for Molecular Recognition and Synthesis, Department of Chemistry, Fudan University, Shanghai, 200433, PR China. masm@sioc.ac.cn.
⁵ State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai, 200032, PR China. masm@sioc.ac.cn.

^# Contributed equally.

Abstract

Stereoselectivity control and understanding in the metal-catalyzed reactions are fundamental issues in catalysis. Here we report sterically controlled rhodium-catalyzed S_N2'-type substitution reactions of optically active tertiary propargylic alcohols with arylmetallic species affording the non-readily available enantioenriched tetrasubstituted allenes via either exclusive syn- or anti-β-OH elimination, respectively, under two sets of different reaction parameters. Detailed mechanistic experiments and density functional theory (DFT) studies reveal that the exclusive anti-Rh(I)-OH elimination is dictated by the simultaneous aid of in situ generated boric acid and ambient water, which act as the shuttle in the hydroxy relay to facilitate the Rh(I)-OH elimination process via a unique ten-membered cyclic transition state (anti-TS2_u). By contrast, the syn-Rh(III)-OH elimination in C-H bond activation-based allenylation reaction is controlled by a four-membered cyclic transition state (syn-TS3) due to the steric surroundings around the Rh(III) center preventing the approach of the other assisting molecules. Under the guidance of these mechanistic understandings, a stereodivergent protocol to construct the enantiomer of optically active tetrasubstituted allenes from the same starting materials is successfully developed.