Sodium dithionite initiated regio- and stereoselective radical addition of polyfluoroalkyl iodide with norbornene analogs

Abstract

Sodium dithionite initiated free-radical addition of polyfluoroalkyl iodides ( 2m– 2s) with norbornene 1a and its derivatives, such as norbornene-2-carboxylates 1b and 1c, and norbornene-2-carboxylic acids 1d and 1e was investigated. In all the cases, the addition of R F group was stereoselectively delivered at exo-position and the predominant configuration of products was trans. Under the similar condition, norbornene-2-carboxylic ethyl ester 1b reacted with 2p to give 6- exo-R F-5- endo-iodo adduct 3bp and 5- exo-R F-6- endo-iodo adduct 5bp in the ratio of 4:1. While 1c, which has a heavy crowded group in the 2- endo-position, gave 6- exo-R F-5- endo-iodo adduct 3cp and polyfluoroalkylated product 4cp retaining the trans-configuration and the exo-orientation of R F group. The fluoroalkylation–lactonization reaction occurred in the reaction of norbornene-2- endo-carboxylic acids 1d and 1e with polyfluoroalkyl iodides to afford the corresponding fluoroalkylated γ-lactone products ( 7dp– 7ds, and 7em– 7er). The configuration of the products was further confirmed by 2D NMR and X-ray diffraction analyses for the first time.