Coniine, the highly toxic alkaloid found in poison hemlock (conium maculatum), I found out, is 2-propylpiperidine, I myself have not yet the experience nor the knowledge to have any idea how exactly,
but maybe some wiser bees might be able to come up with a way to produce piperidine, using the poison hemlock that grows wild in abundance as a source?
That's the worst idea I've ever heard, since the suggestion of using atropine as a possible starting-point for cocaine synthesis.
I'll rather extract it from black pepper then ,if I was you..
Next to that, it is not possible to go from 2-propylpiperidine __> piperidine.