Synthesis of S-thioacyl dithiophosphates, efficient and chemoselective thioacylating agentsProofs for the reversibility of isomerisation of anhydrides 1 to 2, melting points of amides and thioamides obtained from anhydrides 5–7 and 1H, 13C NMR and IR data of isolated anhydrides 5–7, 17 are available as supplementary data. For direct access, see http://www.rsc.org/suppdata/p1/b2/b201233b/

Easily available acyl dithiophosphates are not stable and isomerise reversibly to O-thioacyl monothiophosphates, especially when subjected to heating. Much slower but probably irreversible isomerisation to S-thioacyl monothiophosphates occurs. Since equilibrium states are established and S-thioacyl (mono) thiophosphates form slowly, reaction mixtures contain generally both thioacylating and acylating agents, and consequently cannot be used for efficient thioacylation. On the other hand, treatment of a mixture of isomeric anhydrides with an excess of a dithiophosphoric acid leads to exclusive formation of S-thioacyl dithiophosphates. They appear to be excellent thioacylating agents: relatively stable, inert towards water and oxygen and therefore easy to handle. Reactions with nitrogen or sulfur nucleophiles proceed very rapidly under ambient conditions, yielding respective thioacyl derivatives. Isolation of the products is very simple. Due to the low reactivity of S-thioacyl dithiophosphates towards oxygen nucleophiles they can be used for direct thioacylation of multifunctional nucleophiles with unprotected hydroxy groups. Respective thioacyl derivatives cannot readily be obtained using other methods.