A stereoselective versatile synthesis of 3‐(2,2‐ dihalovinyl)‐2,2‐dimethylcyclopropanecarboxylic acids

A straightforward high‐yield synthesis of cis‐3‐(2,2‐dihalovinyl)‐2,2‐dimethylcyclo‐propanecarboxylic acids is described which uses only inexpensive starting materials and reagents. The synthesis of these acids, involving a [2+2]‐cyclo‐addition of halogenated ketenes with 2‐methylpropene and two rearrangements (the ‚cine’︁ and the Favorskii rearrangements) as the key steps, exemplifies the conceptually new synthesis.