Nucleophilic Reactivity of the Thiophosphoryl Group

The difference in the nucleophilic reactivities of the and groups can be satisfactorily explained on the basis of Pearson's acid‐base concept[21]. The thiophosphoryl sulfur is a typical “soft base”, and reacts preferentially with sub‐group B metals, halogens, and sp3 hybridized carbon, whereas it is largely inert to “hard acids” such as protons, carbonyl carbon, and tetrahedral phosphorus. Since a nucleophilic attack by the thiophosphoryl sulfur leads to a decrease in the charge density of the phosphorus atom, the latter (or the α‐carbon atom in O‐alkyl esters) becomes more open to nucleophilic attack. This reaction principle forms the basis of sulfur exchange, dealkylation, isomerization, and the Pistschimuka and Michalski reactions.