Unusual reactivity of 3-chloro-1-pentafluorosulfanylpropene in nucleophilic substitution reactions

Treatment of 3-chloro-1-pentafluorosulfanylprop-1-ene 1 with KCN yielded the product of prototropic rearrangement CICH=CHCH2SF5, whereas reactions with NaN3 and KSCN gave the SN2 products. Ab initio calculations at MP2/6-311++G** level are used to explain the unusual behaviour of cyanide. It was found that proton transfers from both 1 to CN- and from HCN to the anion of 1 are exothermic. In contrast, azide and thiocyanate ions are too weakly basic to deprotonate 1. (c) 2005 Elsevier Ltd. All rights reserved.