Butane is the only carbon source allowed.
My attempt thus far: I noticed that there are 12 carbons, with butane being my starting material I decided to break it up into three butane groups. One butane group I chlorinated and then used H20 to make butanol, I figured I could later turn it into the ketone with something like Na2Cr2O7. I'm unsure how to proceed now. I can't seem to get the corey-house to work and this is the only method I know to connect smaller alkanes.
Synthesizing 5-propyl-4-nonanone from butane.