Carbocationoids, a concept for controlling highly reactive cationic species.

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.

Development of a Storable Triazinone-Based Reagent for O- p-Methoxybenzylation under Mild Heating Conditions.

A new triazinone-based reagent for O- p-methoxybenzylation has been developed. In spite of its stability in solid form, this reagent converts a free alcohol into the corresponding p-methoxybenzyl ether with mild heating (50-60 °C) in a solution. High functional group tolerance can be achieved because the reaction does not require the addition of an acidic or basic activator.

Triazine-Based Cationic Leaving Group: Synergistic Driving Forces for Rapid Formation of Carbocation Species.

A new triazine-based cationic leaving group has been developed for the acid-catalyzed alkylation of O- and C-nucleophiles. There are two synergistic driving forces, namely, stable C═O bond formation and charge-charge repulsive effects, involved in the rapid generation of the carbocation species in the presence of trifluoromethanesulfonic acid (∼200 mol %). Considerable rate acceleration of benzylation, allylation, and p-nitrobenzylation was observed as compared to the reactions with less than 100 mol % of the acid catalyst. The triazine-based leaving group showed superior p-nitrobenzylation yield and stability in comparison to common leaving groups, trichloroacetimidate and bromide. A plausible reaction mechanism (the cationic leaving group pathway) was proposed on the basis of mechanistic and kinetic studies, NMR experiments, and calculations.