Fig. 2: Mechanistic aspects of the reaction. | Communications Chemistry

Fig. 2: Mechanistic aspects of the reaction.

From: A protocol for controlled reactivity shift in the 2,2-difluorovinyl motif used for selective S–18F and C–18F bond formation

Fig. 2

The reaction in our understanding follows the SET oxidation route. Competing E2 elimination (A) leads to the formation of [18F]1a; irreversible protonation is too slow (B); oxidation of the carbanion (C, D) is the actual rate-limiting step, as a result, fluoride is trapped in the product (D) via a radical intermediate. Overoxidation (E) (pathway I) suppressed [18F]1b formation via radical shift (F) and dissociation (G), to form sulfonyl fluoride that is hydrolysed to toluenesulfonic acid (or esters, H), liberating fluoride ion in the process. Due to the fast reaction rate of the SET mechanism (Pathway I: C, F, G and Pathway II: C, D), both [18F]1b and sulfonyl [18F]fluoride can be obtained in n.c.a. quality now.

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