“…In fundamental work by Severin, it was shown that chlorination, bromination, and iodination of α,β-unsaturated hydrazones, 16 semicarbazones, and oximes 17 regioselectively afford the C3 halogenated products in moderate yields. When analyzing Severin's reported sequence in more detail, we realized that (1) the introduction of the hydrazones was impractical due to the necessity of elevated temperatures in combination with long reaction times, (2) both the hydrazone and the halogenated product had to be isolated due to the incompatibility of the solvents and reaction conditions used for each individual step, (3) harsh conditions (hydrobromic acid, aqueous formaldehyde) were involved for the cleavage of the hydrazone, and (4) some of the used reagents were expensive (2-methyl-benzothiazolinone hydrazone) or inherently incompatible with aprotic organic solvents (semicarbazide).…”