Addition of Semidione Radicals to Arenediazonium Ions: Synthesis of 1,1-Diacyl-2-arylhydrazines

Article abstract of DOI:10.1021/jo00024a021

The α-dicarbonyl compounds 1 are selectively reduced to semidione radicals 2 by aqueous Ti³⁺, via inner-sphere electron transfer (ET).When an equimolar amount of an arenediazonium salt (3) is present, 2 adds to the nitrogen-nitrogen triple bond of 3 to afford the intermediate azo radical cation C, which, depending on the nature of the para substituent of the N-phenyl ring, undergoes rearrangement to a 1,1-diacyl-2-arylhydrazine (4) or preferentially reduction to a hydrazone (5).A mechanism that accounts for both the rearrangement and the substituent effects that are observed is proposed.