Intramolecular Anodic Olefin Coupling Reactions: Using Radical Cation Intermediates to Trigger New Umpolung Reactions

Abstract

Anodic electrochemistry is a powerful tool for generating radical cation intermediates and initiating new cyclization reactions. Like most electrochemical reactions, the transformations involve umpolungs. In this review, recent studies examining the intramolecular coupling of radical cations derived from enol ethers, vinyl sulfides, and ketene acetals with carbon, oxygen, and nitrogen trapping groups are discussed to highlight their synthetic potential.

1 Introduction and Background

2 Arteannuins: A Backdrop for Discovery

3 A Detour: Ketene Acetals as Anodic Olefin Coupling Partners

4 Continuing the Detour: Ineleganolide and a Revised Working Model

5 Extending the Model: Nitrogen Trapping Groups

6 Back to Arteannuins: Completing the Ring Skeleton

7 Lactone Targets and a Couple of Final Points

8 Conclusions

Key words

electron transfer - radical cation intermediates - umpo­lung - cyclizations

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  In this case, the potential was measured for a ketene acetal derived from undecanoic acid. For the oxidation potential of an enol ether, see:

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23

Potentials were measured using Pt working and auxiliary electrodes, an Ag/AgCl reference electrode, an electrolyte solution of 0.1 M LiClO₄ in MeCN, a sweep rate of 25 mV/s, and a substrate concentration of 0.025 M. The reference electrode was calibrated using ferrocene as a standard.

25

For previous examples and a brief discussion, see refs. 24 and 19c.

31

For a prior example, see ref. 20a.