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

• Published in: Tetrahedron Vol. 62; no. 43; pp. 10091 - 10099
• Main Authors: Wu, Fanhong, Xiao, Fanhua, Yang, Xianjin, Shen, Yongjia, Pan, Tieying
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 23.10.2006; Elsevier
• Subjects: Chemistry; Chemistry, Organic; Physical Sciences; Science & Technology; SULFINATION
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/j.tet.2006.08.042

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. Sodium dithionite initiated free-radical addition of norbornene and its derivatives with polyfluoroalkyl iodides was investigated. In all the cases the addition of R F was stereoselective at exo-position and the predominant configuration of products was trans. Norbornene with a high steric hindered group in the 2- endo-position gave 6- exo-R F-5- endo-iodo adduct and deiodined product. Fluoroalkylation–lactonization occurred in the addition of norbornene-2- endo-carboxylic acid with R FI to afford fluorinated γ-lactone products. [Display omitted]