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Rapid Conversion of Hindered Arylsulfonates



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Rapid Conversion of Hindered Arylsulfonates to Alkyl Chlorides with Retention of Configuration TABLE 1 Reaction of Various Sulfonate Esters with TiCl4 Leading to Alkyl Chlorides Salvatore D Lepore Anjan K Bhunia Deboprosad Mondal Pamela C Cohn and Craig Lefkowitz Department of Chemistry Florida Atlantic UniVersity Boca Raton Florida 33431 0991 slepore fau edu ReceiVed NoVember 10 2005 Arylsulfonates of hindered secondary alcohols are converted to the corresponding alkyl chlorides very rapidly and in good yields in the presence of titanium tetrachloride at low temperatures These reactions proceed with exclusive retention of configuration We are interested in the development of highly efficient leaving groups containing chelating units capable of attracting incoming nucleophiles We envision that electrophiles containing sulfonate leaving groups could be rendered more reactive by modifying them to contain a metal chelating moiety 1 In this chelated form the nucleophilic portion of a salt or Lewis acid is localized near the electrophilic center thus decreasing the entropic barrier relative to intermolecular reactions The chelated metal would also be expected to stabilize the developing negative charge on the oxygens of the sulfonate leaving group in the transition state 2 We have recently demonstrated that metal halides react at greatly accelerated rates with arylsulfonate based nucleophile assisting leaving groups NALGs that contain a polyether unit including macrocyclic attached to the aryl ring ortho to the sulfonate 3 In an attempt to further explore the generality of the NALG technology we discovered a highly efficient method to convert NALG sulfonates of hindered alcohols to the corresponding chlorides using TiCl4 at low temperatures While a related chlorination procedure with alkyl tosylates has been reported 4 in this paper we demonstrate for the first b a Isolated yields All chloride products have been previously reported Elimination product also observed 21 1



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