Clarification of the stereochemical course of nucleophilic substitution of arylsulfonate-based nucleophile assisting leaving groups.
Secondary alcohols modified as tosylates, PEG-sulfonates, or quisylates undergo inversion of configuration at the reacting center when treated with lithium halide in acetone at reflux, where the PEG-sulfonates and quisylates are substantially more reactive. In sterically hindered cases, elimination is a competing process. In contrast, when treated with TiCl(4), simple secondary sulfonates give chloride products with partial inversion of configuration. Any observed retention of configuration in a given alkyl sulfonate substrate under these conditions is likely due to neighboring group participation or diastereoselective attack on a carbocation (or ion pair) rather than an S(N)i mechanism.
Braddock
D Christopher
DC
Department of Chemistry, Imperial College London, London SW7 2AZ, UK. c.braddock@imperial.ac.uk
Pouwer
Rebecca H
RH
Burton
Jonathan W
JW
Broadwith
Phillip
P