I have a paper on similar cyclizations, using the analagous scheme.
where piperidine methanols are formed.
according to the NMR data in that paper, no tetrahydropyridines are produced what more proof do you need.
If you are sceptical you can always be sure by doing thin layer chromatograghy analysis.
Methods and Results
The structures of the unknowns were elucidated and their identities confirmed: MPPP and MPTP. The composition and appearance of the powders from the various sources varied: the sample from the San Jose patients was white and contained primarily MPTP; the Santa Cruz County sample was brown and was a mix of MPPP and MPTP. The powder taken during the fire inspection of the illicit lab contained MPTP with only a trace of MPPP.
Data obtained by the DEA Lab and the Lab of Criminalistics for the detection of and identification of MPPP and MPTP include the following: color tests may provide some information initially; Marquis reagent produces a red violet to blood red color, depending on concentration; there is no color with Mecke reagent; the cobalt thiocyanate test gives a blue color (chloroform soluble) [5]. The TLC system utilizes Merck silica gel 60 F254 plates developed in a chloroform methanol mixture (4:1). The spots may be visualized with either iodoplatinate spray or Marquis reagent streaked on the plate. The synthetic intermediate HPMP, migrates to Rf 0.12, MPTP to Rf 0.29, MPPP to Rf 0.40. All three give brown red spots with Marquis. The iodoplatinate spray reacts with the HPMP and the MPPP to give purple spots that dry to purple-brown; MPTP turns blue/black and dries to purple [5]. An alternative system uses Merck silica gel plates developed in a mix of methanol and phosphate buffer at pH 4 (100:1): MPTP migrates to Rf 0.24 and MPPP to 0.31.
GC at the Lab of Criminalistics was performed on a 6’ (1.8mm) glass column packed with 2.5% SE-30 at about 200*C. Under these conditions, meperidine elutes at 3.5minutes, MPPP at 3.65 minutes, and MPTP at 1.55minutes. The compounds may also be detected on 3% OV-1 (at 160*C) or OV-17 (at 190*C) columns: on the former elution times are MPTP at 1.19, HPMP at 1.45, meperidine at 3.28 and MPPP at 3.33minutes. Thermal decomposition may be a problem on these columns.
The infrared spectrum of MPPP contains peaks at approximately 700, 770, 880, 910, 1050, 1160, 1190, 1470, 1745, and 2500 to 2600 wave numbers. The peaks at 770, 1190, and 1380 may occur with or without splitting. The infrared (IR) spectrum of MPTP contains major peaks at 690, 755, 820, 960, 1090, 1150, 1200, 1430, 2500 to 2700, and 2750 wave numbers. The mass spectrum of MPPP has major (in order of decreasing magnitude) at 173, 172, 96, 91, 77, 103, 174, 115, 57, 70, 130, 129, 144 and 82 amu [5].
According to some forensic chemists (thanks DEA!!!)
I'll see about sending the pdf to Rhodium so he can post for you doubters.
The method used that produced MPTP was the method of Zeiring and Lee.
That involves acetic anhydride acylation of a tertiary piperinol catalyzed by H2SO4 (Bad idea! since both are strong dehydrating reagents, and the teriary alchols are the easiest to dehydrate.)
this method doesn't suffer from these diadvantages.
P.S. BWITI I'll get those papers I promised you regardring cyclization mechanism forming the piperidine reversed esters, and the analagous article proving the improbability of MPTP formation going this route, I have been incarcerated lately and unable to accomadate you.
not only is that chromatographic data useful but it also provides the solvent pair for column chromatography and the preferred media (silica) now all we need to know are the parameters, the type of silica and mesh size, column dimensions, etc, by inference one can reasonably conclude that the CHCl3/methanol sovent pair is optimal for chromatographic resolution considering the rf spreads betwwen that and the MeOH/phosphate buffer system.
this suggests methanol is a better solvent for MPTP than Chloroform.
So if you chromatograph it with straight chloroform you may be able just to elute the column with ChCl3 to obtain pure MPPP leaving the MPTP absorbed onto the silica.
to be confimed by tlc of course.
this can be deterimed expirimentally and cofirmed by Thin layer chromatography analysis of the eluted fractions.
Or the "Journal of chromatography" may become your best friend for the next few weeks.
on a side note the piperidone route is still viable and safe if the proper modifications are employed there are several possibilities but I'll give only one.
when Phenyl Lithium adds to the piperidone, the oxolithium compund of the 4-phenyl-4-pieridinol arises.
on hydrolysis the alchol is furnished along with LiOH.
the alternative is to acylate the oxolithium compound ROLi with either propionyl chloride, or propionic anhydride in ether/thf (Thf prefered because of it's unsterically hindered lone pairs of electrons are able to complex and solvate the oxolithium compound) forming the reversed ester and either lithium chloride and the reversed ester, or in the latter case, lithium propionate and the reversed ester.
since the oxo lithium compound is an alkoxide it does not undergo elimination as H2O does therby precluding the possiblility of MPTP being formed.
