There was some interest in the .PDF Journal Article I posted regarding synthesis & pharmacology of Longer Acting Fentanyl Analogues.
I also have the .PDF for a journal article regarding the synthesis & pharmacology of 4-Methyl Fentanyl. This analogue is approximately 3x the potency of Fentanyl and has significantly better confidence limits. The journal article is by I.V. Micovic et al. - the same group who published the article about 2,3-secofentanyl available at Rhodium's site.
In this article this article they use a different method to the more common N-alkylation of 4-piperidone, formation of imine derivative of N-alkylpiperidone followed by reduction of imine derivative etc. The method presented is also suitable for the synthesis of other 4-substituted fentanyl derivatives, which range between 2x and 30x the activity of Fentanyl.
I don't have the ability to put the .PDF online, but if bees express some interest in this article I can email it to Rhodium, who can make it available.
...Anansi