I bet N,a-dimethyl - cyclohexa[3,4]diene-ethylamine (propylhexedrine but with a double bond between position 3 and position 4 in the ring) would be one hell of a fun stimulant. Since the ring would be more rigid, it would be more potent at CNS catecholamine release than propylhexedrine is, and likely less strongly peripherally adrenergic... simply because it bears an even closer resemblance to methamphetamine.
First we've gotta keep in mind that the shit in the inhalers is racemic propylhexedrine. Enatiopure d-propylhexedrine would probably be less harsh than Benzedrex on the PNS because the l-propylhexedrine is undoubtedly adding significant adrenergic PNS activity without adding appreciable CNS activity. D-propylhexedrine would likely feel cleaner than the racemic found in Benzedrex inhalers and would be about 2x more potent, but still far short of d-methamphetamine in potency.
d-N,a-dimethyl - cyclohexa[3,4]diene-ethylamine ... now this would would probably be pretty kickass. I bet it could beat racemic amphetamine and even give enatiopure d-amphetamine a run for its money. If I had to guess, I'd guess that 30 mg d-propylhexedrine = 8.5 mg d-methamphetamine = 15 mg N,a-dimethyl - cyclohexa[3,4]diene-ethylamine ... the latter being our never tasted by humans compound; propyl but with a double bond at pos 3,4 on the ring.
I think it's possible that 3,4-methylenedioxy - N,a-dimethyl - cyclohexa[3,4]diene-ethylamine --
[that name is almost def TOTALLY wrong by IUPAC conventions most likely, but I think it conveys what I mean just fine]
-- could possibly have entactogenic and empathogenic activity similar to MDMA but perhaps less potent.
This molecule is basically propylhexedrine but with the bond between positions 3 and 4 on the ring changed from a single bond to a double bond. The lone two hydrogens that are left sticking off one on position 3 and one on position 4 are replaced with the methylenedioxy bridge between position 3 and 4 like in MDMA.
The double bond increases rigidity of the molecule in this region of the molecule, and by extension, increases the locking in of the methylenedioxy bridge into one position, which seems necessary for relatively strong 5-HT releasing activity without extreme toxicity to 5-HT like p-chloro-amphetamine has.
Without the double bond, you'd have to keep in mind that introducing a MD bridge would be a another chiral center (right? ... cuz there's two hydrogens to each carbon at the saturated ring on propylhex... so the MD bridge could be replacing the two H molecules sticking towards the same direction as the a-methyl in 3D space or the MD bridge could replace the two H molecules facing away / in the other direction from the a-methyl in 3D space. I seriously doubt either isomer would be active, nor would, by extension, a racemic mixture of this compound.
But with a double bond at pos 3,4 the situation is more similar to methamphetamine being subbed with an MD bridge at 3,4. It's still not as planar and rigid as MDMA's ring region would be, but it's closer (more rigid and planar) than the propyl racemic mixture by far.
I really think the compound 3,4-methylenedioxy - N,a-dimethyl - cyclohexa[3,4]diene-ethylamine probably has activity. Whether you just end up with just another stimulant like propylhexedrine and methamphetamine or an MDMA like empathogen/entactogen I can't say for sure.
However, some of the sensations during the propylhexedrine experience suggest significant 5-HT efflux compared to amphetamine -- 5-HT efflux more akin to methamphetamine.
An MD bridge at 3,4 on propyl would muck up everything by having two new isomers and both isomers having the MD bridge jut out in a way that probably destroys activity.
However 3,4-methylenedioxy - N,a-dimethyl - cyclohexa[3,4]diene-ethylamine is more rigid and planar at 3,4 and that MD bridge creates no chiral center because the double bond leaves each carbon 3 and 4 to only make one bond like in the aromatic ring. The MD bridge also wouldn't jut out way to the side like the cyclohexane ring propyl analog. While not as nice and planar as MDMAs ring area, it's a great improvement.
And I was just thinking since propylhexedrine already seems to cause more 5-HT efflux based on subjective feelings under its influence, this 3,4-methylenedioxy - N,a-dimethyl - cyclohexa[3,4]diene-ethylamine analog without the conformation issues could be a decent MDxx like entactogen and empathogen.