Nierenstein reaction

The Nierenstein reaction is an organic reaction describing the conversion of an acid chloride into an haloketone with diazomethane.



Reaction mechanism
Like the related Arndt-Eistert reaction, this reactions proceeds through a diazoketone intermediate (5). The loss of nitrogen to gives the desired haloketone (2).



The synthesis of benzyl chloromethyl ketone from phenylacetyl chloride in fact requires the addition of HCl gas to the diazoketone intermediate for it to succeed. The unassisted reaction failed.

Scope
One original 1924 Nierenstein reaction:



and a reaction starting from benzoyl bromide going haywire with formation of the dioxane dimer: