Nucleophilic Substitution Reactions of Neopentyl and Neophyl Iodides with 2-Aryl-1,3-Dithiane Anions

OKSDATH MANSILLA, G. Y PEÑÉÑORY, A. B.

Argentina

Conferencia; 9 Conferencia Latinoamericana de Fisicoquímica Orgánica; 2007

IX CLAFQO

1,3-Dithiane anions are often used as acyl anion equivalents for C-C bond forming reactions,1 which is a common and successful strategy for the construction of complex natural products.2 These anions react with common electrophiles such as alkyl, allyl and benzyl halides, aldehydes, ketones and carboxylic acid derivatives by polar mechanisms. Furthermore, the participation of 2-lithio-1,3-dithiane as electron donor was suggested in the reaction with a neopentyl-type radical probe 5,5-dimethyl-6-iodo-1-hexene, with formation of 6-11% of cyclized alkylated product.3 These reactions were performed at very low temperature (-20°C) in THF or THF-TMDA as solvent, and a chain process was disregarded. To further explore the possibility of dithiane anions as electron donors in a radical nucleophilic substitution (SRN1),4 we have studied the reactions of 2-aryl-1,3-dithiane anions (1) with neopentyl (2a) and neophyl (2b) iodides under a variety of conditions in DMSO at 20°C. Thus, 1     (Z = H) reacts with iodide 2a to afford the substitution product 3a, in 50% yield. On the other hand, the neophyl iodide (2b) after 1h yields mainly the unrearranged substituted product 3b. Evidences for the operating mechanism will be presented and discussed.   References 1. (a) Seebach, D.; Corey, E. J. J. Org. Chem.1975, 40, 231-237; (b) Seebach, D. Angew. Chem. Int. Ed. Engl. 1979, 18, 239-258. 2.  (a) Smith, A. B. III; Adams, C M. Acc. Chem. Res. 2004, 37, 365-377; (b) Yus, M.; Nájera, C.; Fourbelo, F. Tetrahedron 2003, 59, 6147-6312. 3. Juaristi, E.; Jiménez-Vásquez, H. A. J. Org. Chem. 1991, 56, 1623-1630.  4. R. A. Rossi, A. B. Pierini, A. B. Peñéñory, Chem. Rev. 2003, 103, 71-167