Nucleophile assisting leaving groups: a strategy for aliphatic 18F-fluorination.

A series of arylsulfonate nucleophile assisting leaving groups (NALGs) were prepared in which the metal chelating unit is attached to the aryl ring via an ether linker. These NALGs exhibited significant rate enhancements in halogenation reactions using metal halides. Studies with a NALG containing a macrocyclic ether unit suggest that rate enhancements of these nucleophilic halogenation reactions are facilitated by stabilization of charge in the transition state rather than through strong precomplexation with metal cation.

Rapid conversion of hindered arylsulfonates to alkyl chlorides with retention of configuration.

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.

Arylsulfonate-based nucleophile assisting leaving groups.

[Chemical reaction: See text] The synthesis and unique reactivity of a series of arylsulfonate-based nucleophile assisting leaving groups (NALG) containing oligomeric ether units (including crown ethers) attached to the arylsulfonyl ring in the ortho orientation are described. The reactions of a variety of these ether-containing alkyl sulfonates with metal halides proceeded at substantially greater rates than electronically similar sulfonates. These ether-containing leaving groups also displayed marked selectivity for lithium halides relative to the corresponding sodium and potassium salts in nucleophilic displacement reactions.