Arylation of diversely substituted hydrazines by tri- and pentavalent organobismuth reagents

Various hydrazine derivatives were studied with respect to arylation by triarylbismuthane and triarylbismuth diacetate reagents with emphasis on scope and limitations. Among these reagents, a few contained bulky substituents in their aromatic rings. The applied substrates spanned a range from simple hydrazides to triply protected hydrazines and included a large number of intermediates of principal synthetic interest. In the case of mono- and disubstituted hydrazines the results demonstrate apparent advantages of pentavalent over trivalent reagents, exemplified by fast, highly chemoselective monoarylation of acylhydrazines at the terminal nitrogen. In contrast, trisubstituted hydrazines are more efficiently substituted by trivalent reagents. With these substrates, a strong influence of steric factors was occasionally observed, as reflected in lower yields and even complete reaction inhibition. The introduction of two different aromatic substituents into disubstituted hydrazines using step-by-step or one-pot procedures was accomplished.