Part A - Preparation of 1,3-Cyclopentadiene
Place 20mL of dicyclopentadiene in a 100-mL rbf, and attach the flask to a fractional distillation apparatus that is equipped with an ice-cooled receiver and has an unpacked fractionating column. Using either a small burner or heating mantle, gently heat the dimer until brisk refluxing occurs (Caution : occastional foaming) and the monomer begins to distill in the range of 40-42°C. Distill the monomer as rapidly as possible, but do not permit the head temperature to exceed 43-45°C. About 6g of monomer should be obtained after distillation for about 30 min. Terminate the distillation when approximately 5g of residue remains in the flask. If the distilled 1,3-cyclopentadiene is cloudy because of condensation of moisture in the cold receiver, add about 1g of anhydrous calcium chloride to dry it.
1,3-Cyclopentadiene is a mildly toxic and rather volatile substance. Prepare and use it in a hood, if possible. Keep the diene cold at all times to minimize vapourization and possible inhalation of its vapour.
Part B - Reaction of 1,3-Cyclopentadiene with p-Benzoquinone
Prepare dry 1,3-cyclopentadiene as described in part A. Add a solution of 3,2g (4,0mL, 0,049 mol) of this diene and 10mL of toluene to 2,7g (0,025 mol) of p-benzoquinone1 dissolved in 20mL toluene, and swirl the resulting solution until the mildly exothermic reaction has subsided. After 1h cool the reaction mixture to 0°C and filter to isolate the solid adduct.
In order to collect a second crop of product, concentrate the mother liquor to one-third of its original volume by distillation, cool the pot residue, collect the precipitate, and wash it with a few milliliters of ice-cold toluene. Combine the two crops of adduct and recrystallize the product by dissolving it in a minimum amount of boiling acetone and then adding water until turbidity begins to appear in the boiling mixture. Clarify the solution by addition of a small amount of acetone and allow the solution to cool slowly to room temperature. Complete the recrystallization by cooling the solution to 0°C.
The pure adduct forms beautiful iridescent white needles or platelets and has a reported melting point of 157-158°C. The expected yield is 60-70%.
1 Commercial p-benzoquinone is generally rather impure and may require purification prior to use. However, a grade of this chemical having mp 113-115°C can be used without further purification. The quinone can be purified by sublimation...This was from Robert's "Modern Experimental Organic Chemistry" 390(1969). It's pretty standard stuff, SWIM just introduced it in the hopes of lighting a match under this thread's ass
. Instead of using 2 mol 1,3-cyclopentadiene per 1 mol benzoquinone, you would want to use a 1:1 ratio (or perhaps a slight excess of benzoquinone?) so the cyclopentadiene doesn't add to both sides. After that you'd need to reduce the double bonds before the methylation that Shulgin describes (maybe Urushibara or Zn/HCl??). Ideas are welcome.
Cycloadditions of dienes looks very interesting. Maybe other suitable dienophiles aside from benzoquinone could be used for patterns other than the 2,5-dimethoxy? What is the commercial name for cyclohexadiene-1,2-dione (maybe bridge something instead of having methoxys)?
How does one go about selecting a suitable diene for a specific dienophile? Obviously any diene wouldn't do depending on the structure your going for. 1,3-Cyclohexadiene, 1,3-butadiene (SWIM can offer an insitu preparation of this bp -4,4C from 3-sulpholene), as Rhodium said thioprene and possibly a benzfuran sort of thing with furan. These could all be potent compounds too; SWIM isn't sure if Osmium was being sarcastic or not, but just imagine being high for weeks! 20mg down the hatch, no need to re-dose, you peak for 4-5 days, then come down over a week. It would be absolutely exhausting, super!
Finally, the formylation procedure is where an OTC chemist would get stuck. SWIM would really like to get into a discussion on the possibility of a chloromethylation. Does anyone think that it wouldn't work???
Post 384897
(Rhodium: "Chloromethylation of p-dimethoxybenzene - 61%!", Methods Discourse) seems like it might work, anybody (somebody please
) want to discuss it??
It's ashame the "structural tour of pihkal" piece only devotes a paragraph to this stuff. SWIM isn't fully comfortable with the chemistry involved in these compounds. It'll only be a matter of time though
. Did Shulgin make these compounds late in his career? It doesn't seem that he was very intriguied by them, pity.
[sigh]Only if SWIM had his/her own island, with their own lab, all the precursors they would ever want and no interuptions.[/sigh] SWIM would consider that a good life.
