As you remember, during World War I, the Germans are unable to make methyl isoprene the easy way, from acetone and aluminum, because those raw materials are needed for explosives and aircraft manufacture. This forces the German chemists to come up with a round about way of synthesizing the monomer for the much needed methyl rubber. They start with coal and lime, two raw materials Germany has a lot of.
First, they heat the coal and lime together to produce calcium carbide. Water is added to the calcium carbide to produce acetylene. The acetylene is reacted with still more water in the presence of a mercury salt, and acetaldehyde is formed. This is simply oxidized to acetic acid, which is then heated with more lime to form calcium acetate. The calcium acetate is dry distilled to make acetone.
Well, that was painful, but we're not done yet. Some of the acetone made from the above process is used for making explosives, but most of it goes on to become methyl isoprene through the much shorter process mentioned at the top of the page.
The acetone is treated with an aluminum salt and caustic soda to form an aluminum salt of pinacol. This salt is then simply distilled under pressure to form the much needed methyl isoprene.
From Wolf, Howard and Ralph. Rubber: A Story of Glory and Greed. New York: Covici, Friede, 1936.