# Carbocationoids, a concept for controlling highly reactive cationic species

## TL;DR

A new two-step method controls unstable carbocations for efficient alkylation reactions without cross-reactivity.

## Contribution

A two-step SN1 reaction strategy using nucleophile-free carbocation accumulation avoids nucleophile-activator interference.

## Key findings

- Carbocationoids are stabilized in a nucleophile-free solution using triazinediones.
- Room-temperature alkylation is achieved without acidic additives in the second step.
- The method enables alkylation of diverse neutral nucleophiles under mild conditions.

## Abstract

Carbocations, which are positively charged highly electrophilic intermediates, are efficacious for the direct alkylation of low-reactive nucleophiles. The utilization of carbocations in SN1 reactions relies on the activation of their precursors in the presence of a nucleophile. However, undesirable interactions between the nucleophile and the leaving group activator limit the scope of acceptable nucleophiles. Here we report a strategy to conduct SN1 reactions involving unstable carbocations in an alternative stepwise procedure, which was demonstrated by the benzylation of various neutral nucleophiles. In the first step, carbocations were accumulated in a nucleophile-free solution in the form of carbocationoids utilizing the coordinative stabilization of triazinediones. Subsequently, the addition of these solutions in the second step enabled room-temperature alkylation without the need for acidic additives. This methodology overcomes the inherent challenges of carbocations in SN1 reactions.

Carbocations are highly electrophilic intermediates involved in SN1 reactions, such as the direct alkylation of low-reactivity nucleophiles, however, in situ activation of leaving groups in such reactions remains challenging due to the unstable nature of the carbocations, leading to cross-reactivity between nucleophiles and leaving group activators. Here, the authors develop a two-step procedure to avoid such cross-reactivity: they generate carbocationoids as coordinatively stabilized carbocations in one nucleophile-free solution, and then complete the alkylation in another reaction vessel under mild conditions.