Beta-hydroxyfentanyl

[Cyrax]

Does someone has some information about:
 * beta-hydroxyfentanyl
 * beta-hydroxy-3-methylfentanyl
How powerfull are they, compared to fentanyl?

I found on the web somewhere that beta-hydroxy-3-methyl-thiofentanyl is 1500 times as powerfull as morphine (15 x fentanyl).

I think the only good synthesis would be the reaction of the N-(4-piperidyl)propionanilide (for beta-hydroxyfentanyl) with phenyloxirane.  What do you think about it?  Do you see another synthetic pathway?  Would the addition of the secundary amine to the epoxide give a good yield?

[Cyrax]

Now, I am convinced that this will be a great reaction.

I found in a good organic textbook (Carey: Advanced organic chemistry) a nice example of an similar reaction.
Piperidine reacts with 1,1-dimethyl-2-ethyloxirane with a 100 % yield (whow !).  As expected in a base catalized ring opening reaction, the nucleophile adds to the less substituted carbon.  So, our secondary amine will react nicely with phenyloxirane