Fluorination of tertiary alcohols derived from di-O-isopropylidenehexofuranose and O-isopropylidenepentofuranose

The stereo- and regioselectivity of the dehydroxyfluorination of various tertiary alcohols derived from di-O-isopropylidenehexofuranose and 1,2-O-isopropylidenepentofuranose has been studied. Reactions have been accomplished using DAST and PFPDEA (1,1,3,3,3-pentafluoropropene-diethylamine adduct) as fluorinating reagents. Dehydroxyfluorination of allylic alcohol 2a has occurred with an inversion of configuration and allylic rearrangement leading to two chiral regioisomers 6a and 7a. Analogous reaction of 2b has given allylic chiral fluoride 7b as the only product. In case of phenylacetylene, styryl and benzylic alcohols 3a/3b-5a/5b the single diastereoisomers 8a/8b-10a/10b have been obtained. Additionally, the participation of 1,2-O-substituent effect in carbocation stabilization during fluorination have been discussed.

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► The fluorination of alcohols derived from hexo- and pentofuranose have been studied. Optically pure allylic, propargylic, styryl and benzylic fluorides were prepared. Due to carbocation stabilization by dioxolane in sugar ring stereocontrol was done. Reactions were accomplished by using DAST or PFPDEA.