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Catalytic Hydrothiolation: Counterion-Controlled Regioselectivity.

Xiao-Hui Yang¹, Ryan T Davison¹, Shao-Zhen Nie^1,2

¹Department of Chemistry , University of California , Irvine , California 92697 , United States.

Journal of the American Chemical Society

|February 9, 2019

Summary

This study details catalytic hydrothiolation of dienes, controlling regioselectivity with rhodium counterions. This method enables the first enantioselective synthesis of (-)-agelasidine A from β-farnesene.

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Area of Science:

Organometallic Chemistry
Catalysis
Organic Synthesis

Background:

Catalytic hydrothiolation of 1,3-dienes is crucial for synthesizing allylic and homoallylic sulfides.
Controlling regioselectivity in these reactions remains a significant challenge.

Purpose of the Study:

To expand upon the catalytic hydrothiolation of 1,3-dienes.
To achieve high regiocontrol in the formation of allylic or homoallylic sulfides.
To enable the first enantioselective synthesis of (-)-agelasidine A.

Main Methods:

Utilized rhodium (Rh) complexes with varying counterions (e.g., SbF6-, Cl-).
Investigated mechanistic pathways involving different diene coordination modes (η4 vs. η2).
Performed hydrothiolation of β-farnesene, an essential oil component.

Main Results:

Regioselectivity was dictated by the Rh counterion: non-coordinating counterions favored allylic sulfides (η4-coordination), while coordinating counterions favored homoallylic sulfides (η2-coordination).
Proposed mechanisms rationalizing fractional and inverse thiol dependencies for Markovnikov and anti-Markovnikov pathways.
Successfully synthesized (-)-agelasidine A enantioselectively.

Conclusions:

The choice of counterion is a key determinant for regioselectivity in Rh-catalyzed hydrothiolation of 1,3-dienes.
Developed a mechanistic understanding of thiol dependence in different hydrothiolation pathways.
Established a novel route for the enantioselective synthesis of (-)-agelasidine A.