Heterocyclic compounds hydride transfer

With many heterocycles as substrates, radical substitutions can be successfully carried out under the conditions of phase-transfer Gomberg-Bachmann reactions [145]. Again, as above, mainly aryl and heteroaryl halides have recently been used as precursors for heterobiaryl compounds. A study including the arylation of a large number of heterocycles in the presence of tributyltin hydride and catalytic benze-neselenol led to the results that mostly biaryl products are obtained from nitrogen-containing heterocycles, whereas furan and thiophene gave partially dearomatized compounds [155]. 

Some modifications of amino and hydrazino groups were also performed. An amino group can be replaced in the reaction with amines, although in low yield. To the few known pyridazinonimines some new compounds have been added. The imines (203) are prepared from the corresponding pyridazinium salts and sodium hydride. Hydrazinopyridazines upon nitrosation are transformed into azido- or tetrazolopyrida es. The reaction can be complicated by aza-transfer reactions with a heterocyclic diazo compound. For example, 3-chloro-6-hydrazinopyridazine, when treated with... 

The aim of this chapter is to examine the application of well-defined N-heterocyclic carbene (NHC) complexes, as well as the systems prepared in situ which involve free NHCs or the precursor salt, for the reduction of unsaturated organic molecules such as alkynes, alkenes and carbonyl compounds. The most active complexes for such reactions are based on electron-rich, late transition metals in low oxidation states. Herein, reductions useful for organic synthesis will be classified into four types according to the hydride source used (i) hydrogenations, (ii) transfer hydrogenation, (iii) hydrosilylation and (iv) hydroboration. For examples of reduction reactions with systems containing non-classical NHC ligands, the reader is referred to Chapter 5. 

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