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Demystifying the Soai Reaction

preprint
submitted on 22.07.2019, 18:40 and posted on 23.07.2019, 15:45 by Soumitra Athavale, Adam Simon, Kendall N. Houk, Scott Denmark
The extraordinary Soai reaction has profoundly impacted chemists’ perspective of chiral symmetry breaking, absolute asymmetric synthesis and its role in the origin of biological homochirality. Herein, we describe the unprecedented observation of asymmetry amplifying autocatalysis in the alkylation of 5-(trimethylsilylethynyl)pyridine-3-carbaldehyde using diisopropylzinc. Kinetic studies with a “Trojan-horse” substrate and spectroscopic analysis of a series of zinc-alkoxides that incorporate specific structural mutations reveal a ‘pyridine-assisted cube escape’. The new cluster functions as a catalyst that activates the ‘floor-to-floor’ bound aldehyde and poises a coordinated diisopropylzinc moiety for alkyl group transfer. Transitionstate models leading to both the homochiral and heterochiral products were validated by density functional theory calculations. Moreover, experimental and computational analysis of the heterochiral complex provides a definitive explanation for the non-linear behavior of this system. Our deconstruction of the Soai system contributes substantially to understanding the mechanism of this transformation that has stood as a longstanding challenge in chemistry.

Funding

NIH Chemistry- Biology Interface Research Training Grant (T32GM008496)

History

Email Address of Submitting Author

sdenmark@illinois.edu

Institution

University of Illinois at Urbana-Champaign

Country

United States

ORCID For Submitting Author

0000-0002-1099-9765

Declaration of Conflict of Interest

No conflict of interest

Version Notes

11 May 2019 version

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