Aryl nitriles are important building blocks in modern organic chemistry. They are integral parts of dyes, natural products, materials and agrochemicals. Many transition metals catalyzed or mediated displacements of aromatic halides by the cyanide ion have been developed. The traditional cyanide ion sources are KCN, NaCN, ZnCN, CuCN, (CH3)2C(OH)CN and TMSCN. But these cyanide sources have severe drawbacks: KCN and NaCN are highly poisonous, ZnCN2 and CuCN lead to stoichiometric amounts of heavy metal salt wastes, TMSCN and (CH3)2C(OH)CN are sensitive to moisture. In 2004, Prof. Beller and co-workers described for the first time the use of potassium hexacyanoferrate(II) (K4[Fe(CN)6]) as cyanating agent for the general synthesis of aryl nitriles from aryl bromides. They also found that all the six cyanide ions bound to the iron(II) center are used in the cyanation reaction. Compared with traditional cyanation reagents, potassium hexacyanoferrate(II) is nontoxic and can be handled without special precautions. Various methods for the synthesis of aryl nitriles with this user-friendly cyanating reagent have been developed. Very recently, direct cyanation reactions through transition-metal catalyzed C-H bond activation were reported. This review present the recent development of Pd and Cu catalyzed cyanation reactions with nontoxic and user-friendly potassium hexacyanoferrate(II) as the cyanating reagent.
Contents
1 Introduction
2 Palladium catalyzed cyanation reactions with potassium hexacyanoferrate(II)
3 Copper catalyzed cyanation reactions with potassium hexacyanoferrate(II)
4 Conclusions and outlook