You would imagine they resolved the racemic product into its separate isomers(not that much work in this case), to find out which one displayed that ridiculous potency. The cis isomer would probably be of a much lesser potency. Also something like the related bromadoline would be easier to synth and have a more sensible potency, have you looked into Tapentadol?

Start here I guess:
PROCESS FOR THE PREPARATION OF (1R,2R)-3-(3-DIMETHYLAMINO-1-ETHYL-2-METHYL-PROPYL)-PHENOL
WIPO Patent Application WO/2008/012047
New Link That wont crash firefox (sorry)
You can download the pdf from the above site, linking directly to the pdf crashed firefox when clicked.

Hey Frequency, Heisenberg asked if there were any analogs and there are! I had said it before in this post so may as well say it again;

"Also something like the related bromadoline would be easier to synth and have a more sensible potency, have you looked into Tapentadol?"

Turns out to prepare the correct stereoisomer is not as easy as it seems,
Tapentadol;
is a centrally-acting analgesic with a dual mode of action as an agonist at the u-opioid receptor and as a norepinephrine reuptake inhibitor. It has opioid and nonopioid acitivity in a single compound.
Its dual mode of action provides analgesia at similar levels of more potent narcotic analgesics such as hydrocodone, oxycodone, and meperidine with a more tolerable side effect profile.


From wiki!

Tapentadol is from the same series of analgesics as Bromadol, wiki says the abuse potential is unknown I say its huge! More tolerable side effects than other opoids, with pretty good analgesic activity. Less complicated molecule to synth than traditional opoids, depending on precursors. You get the added norepinephrine reuptake inhibition which potentiates the analgesic effects so less is needed and hence less side effects. The u-opoid receptor activity will make it attractive to opoid addicts, as a substitute when stocks are low. If they started using it intravenously it I am sure it would become very popular very quickly! And its not on the market yet so is not scheduled yet!

edit; With an answer like that, you can see it was legitimately a good question! Most picked it up from me saying "have you looked into Tapentadol", but you must have missed it!

OP, due to the preferential axial attack of the reagent, both your Grignards would produce the wrong isomer in at best a 6:1 ratio, giving you a 2% yield assuming all reactions are quantitative. It's safe to say the target compound in the OP is not for clandestine manufacturers.