Dianionic Phase-Transfer Catalyst for Asymmetric Fluoro-cyclization.

ABSTRACT

Inspired by the dicationic nature of the electrophilic fluorinating reagent, Selectfluor (1), we rationally designed a series of dicarboxylic acid precatalysts (2), which, when deprotonated, act as anionic phase-transfer catalysts for asymmetric fluorination of alkenes. Among them, 2a having the shortest linker moiety efficiently catalyzed unprecedented 6-endo-fluoro-cyclization of various allylic amides, affording fluorinated dihydrooxazine compounds with high enantioselectivity (up to 99% ee). In addition to cyclic substrates, acyclic trisubstituted alkenes underwent the reaction with good diastereoselectivity, whereas low diastereoselectivity was observed for linear disubstituted alkenes. Results suggest that the reaction proceeds via a fluoro-carbocation intermediate.