A new and convenient method is described for the synthesis of hydrazonyl halides. Hydrazones on treatment with N-chlorosuccinimidedimethyl sulfide complex result in the formation of the corresponding hydrazonyl chlorides in good yields. Similarly, treatment of hydrazones with N-bromosuccinimide-dimethyl sulfide complex gives the corresponding hydrazonyl bromide under extremely mild conditions.
Hydrazonyl halides have been the subject of considerable attention during the last few decades. They are considered to be important precursors of nitrile imines, which are used extensively in 1,3-dipolar cycloaddition reactionsL-one of the most versatile methods for the construction of manifold 5-membered heterocycles 2 (Scheme 1). They can also be used to synthesise hydrazones of complex aliphatic ketones directly, by reaction with alkylmetal reagents (R2CH2 M = Li, Zn, Mg, etc, Scheme 1). These hydrazones are important precursors of indoles in the Fisher Indolisation. 3
Aryl hydrazones lb-f possessing a variety of substituents in the aromatic nucleus were converted to the corresponding hydrazonyl chlorides 4b-f in 61-81% yields (Table 1) under similar conditions. This shows that substitution in the phenyl ring of the starting hydrazones exerts no influence on the halogenation; this method can thus be considered to be fairly