Synlett 2018; 29(14): 1807-1813
DOI: 10.1055/s-0037-1610125
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© Georg Thieme Verlag Stuttgart · New York

Deciphering the Redox Chain Mechanism in the Catalytic Alkylation of Quinones

Xiao-Long Xu
School of Physical Science and Technology, ShanghaiTech University, 393 Middle Huaxia Road, Pudong, 201210 Shanghai, P. R. of China
,
Zhi Li  *
School of Physical Science and Technology, ShanghaiTech University, 393 Middle Huaxia Road, Pudong, 201210 Shanghai, P. R. of China
› Author Affiliations
This work was supported by the National Natural Science Foundation of China (Grant No. 21673141), “1000 Talents Plan for Young Professionals” start-up funding, and ShanghaiTech University start-up funding.
Further Information

Publication History

Received: 20 March 2018

Accepted: 03 April 2018

Publication Date:
14 May 2018 (online)


Dedicated to Prof. Hisashi Yamamoto on the occasion of his 75th birthday.

Abstract

Alkylation of p-quinones with allylic and benzylic esters is achieved by using a strong Lewis acid as the catalyst. This transformation likely follows an unusual redox chain mechanism. In this mechanism, quinone undergoes a sequence of reactions: it is reduced to ­hydroquinone (HQ), functionalized in a Lewis acid-catalyzed Friedel–Crafts alkylation, and then oxidized back to quinone. The last step is concurrent with the first step of a second quinone molecule, which is reduced to new HQ and functionalized, and thus propagates the redox chain reaction. The autoinitiation mechanism of the redox chain is not well understood, but additive HQ or Hantzsch ester can serve as effective initiators. The likelihood of this mechanism was elaborated by ­kinetic studies and various control experiments.

1 Introduction

2 Discovery of Catalytic Alkylation Reactions of Quinones

3 Proposed Redox Chain Reaction Mechanism and Experimental Evidence

4 Substrate Scope

5 Conclusion