Pat O’Neill of Pfizer provided the following answer to last month’s challenge.
“I would say that this proceeds via acid catalysed hydrolysis of the enamine to the arylacetaldehyde, followed by alpha chlorination (very activated CH bonds). Finally, the alpha,alpha-dichloroarylacetaldehyde undergoes a facile hydrolysis (like a haloform reaction) to formic acid and the gem-dichloro compound. Alternatively, the dichloroarylacetaldehyde could undergo oxidation by HOCl to the arylacetic acid, which would decarboxylate readily to the same compound.”
This is the second challenge this year for which Pat O’Neill provided the first high quality answers. Thank you, Pat!