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Systematic Synthesis of Multifluorinated alpha,alpha-Difluoro-gamma-lactones through Intramolecular Radical
Toshiyuki Itoh1, Kohei Sakabe, Kazutoshi Kudo
1Department of Chemistry, Faculty of Education, Okayama University, Okayama 700-8530, Japan, Department of Natural Science, Hyogo University of Teacher Education, Yashiro, Hyogo 673-14, Japan, and INRA, Unite de Phytopharmacie et Mediateurs Chimiques, Route de Saint Cyr, 78026 Versailles, France.
Abstract:
Carbon radicals from allyl O-(trimethylsilyl)-alpha-bromo-alpha,alpha-difluoroacetal can cyclize onto the olefinic part regiospecifically to give gamma-lactols in good yield. The lactols are then converted to the corresponding alpha,alpha-difluoro-gamma-lactones. Systematic synthesis of multifluorinated-alpha,alpha-difluoro-gamma-lactones has thus been accomplished through intramolecular radical cyclization as a key reaction. Semiempirical MO calculation study suggested a unique nature of alpha,alpha-difluoroacetate in that complete delocalization of the electrons in the SOMO orbital of alpha,alpha-difluoroacetyl radical occurred; this caused unsuccessful cyclization. To apply the present radical reaction, the first synthesis of both enantiomers of difluoroeldanolide, analogues of the sex pheromone of the male African sugarcane borer, has been demonstrated. Electrophysiological tests revealed that the difluorinated analogues were as active as the natural eldanolide on the olfactory receptors.