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September 12, 2025

Umpolung Approach for the α-Alkylation of Benzylic Amines Enabled by Superelectron Donors

WXWenjuan XiaoNanjing Forestry University WLWen LiuShanghai Jiao Tong University XCXi ChenJiangxi Science and Technology Normal University

Key Points

This method achieves highly efficient α-alkylation of benzylic amines under mild conditions, leading to diverse products.
Utilizing ketimines and alkyl thianthrenium salts, the process demonstrates excellent flexibility in substrates used.
Mechanistic studies reveal that super electron donors facilitate intermolecular electron transfer, crucial for radical formation.
The methodology's potential extends to regioselective alkylation of allylic amines and α-amino acid derivatives.

Abstract

Herein we describe a general transition-metal-free umpolung protocol for the synthesis of α-alkylated benzylic amines. By employing two distinct classes of ketimines and easily available alkyl thianthrenium salts as substrates, this method provides a flexible and straightforward approach to access structurally diverse α-alkylated benzylic amines under mild reaction conditions with high efficiency. Furthermore, this methodology could be extended to the regioselective alkylation of allylic amines and a-amino acid derivatives. Mechanistic investigations suggest that the deprotonated ketimines act as super electron donors (SEDs), engaging in intermolecular single-electron transfer (SET) with alkyl thianthrenium salts to generate key radical intermediates, which play a pivotal role in the base-promoted reaction pathway.

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