[Enthalpy]

Thanks Kriggy! And welcome to totally different approaches!

Up to now I've looked at isobutene, propene, chlorine... because they're cheap, that's the only reason. 1M€/200t would be a reasonable selling price for the oligomerized propellane, so every reactant must be dirt-cheap or recycled (like NCS can be if I read properly).

Malonic acid would be obtained from dimethyl malonate, itself from dimethoxymethane obtained from formaldehyde and methanol, is that it? Or by "fermentation of glucose" as wiki tells? On Alibaba I see malonic acid around 7$/kg in ton amount, that is 13$/kg of isobutene. Maybe production at the plant can improve that?

I suppose AgCl from Hunsdiecker is completely recycled.

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I have a small doubt about the number of remaining carbons after Hunsdiecker.

[kriggy]

I have a small doubt about the number of remaining carbons after Hunsdiecker.

Crap right, hunsdiecker decarboxylats so there is one less carbon for each carboxylate. 
What one could do is do the knovenagel with diethylmalonate, then reduce the ester to alcohol and then halogenate but one more steps.

Anyway, you dont have to use silver salt for the Hunsdiecker reaction. Friend of mine did that few weeks ago, just acid and NBS or acid, sodium acetate and NBS. I suppose that it would be very similar with NCS.

[Enthalpy]

I had botched simply the isobutene on messages #2 and #5, it was worse

Is that what you suggest?
+

Does the reduction need LiAlH₄? I see prices like 200$/kg on Alibaba in ton amount.
Or would alcohol or chlorine suffice for Knoevenagel? Propane-1,3-diol getting a =CH₂ at the middle.
Or eliminate CO₂ by heat somehow? Possibly with the chlorine already in place?

[kriggy]

Basicaly, but why not start directly with dieethyl malonate? Isnt it cheper than to make it on your own?
Im not sure about the reduction, I did it with NaBH4+MeOH but there might be another, cheper systems. maybe even hydrogen reduction could work?

I dont think that alcohol/chlorine would work for Knovennagel, the CH2 is activated by hyperconjugation and none OH or Cl are hypercojugating groups

[Enthalpy]

Diethyl malonate costs about 3$/kg on Alibaba and dimethyl malonate as well, hence is cheaper per mole - but it still converts to 6$/kg of C₅H₈ at 100% yield. This is a concern. And, no, I'm not sure at all that making 400t/month at a plant is cheaper than buying, alas; just the reactants are cheap.

To reduct an ester to an alcohol, I've found the Bouveault–Blanc reduction:
https://en.wikipedia.org/wiki/Bouveault-Blanc_reduction (animation on Spanish and Portuguese pages)
http://www.orgsyn.org/demo.aspx?prep=cv3p0671
with just Na in ethanol. Very promising, isn't it? If the two functions per molecule don't interact in between.

[Enthalpy]

My frenzy in message #13 on May 20 doesn't work, unless someone has a brilliant idea:
CHCl=CH₂ + CH₂BrCl CH₂Cl-CH(CH₂Cl)-CH₂Br
Addition of dichloromethane on alkene has been observed but as anti-Markovnikov
https://www.jstage.jst.go.jp/article/cl1972/7/4/7_4_367/_pdf
out.

My present impression is that the gaseous chlorination of isobutene is the cheapest route, as the reactants are dirt-cheap and the conditions just heat, but will produce gem-dichloro essentially because this radical is easier. So:

would you know chlorinating agents, catalysts, reaction conditions that chlorinate the distant allylic carbons of isobutene preferentially? Possibly a bulky molecule hindered by the first chlorine atom?

NCS seems cheap to regenerate but, said to create Cl₂, it shouldn't show a different selectivity.
HClO? t-ButOCl? Other?

[Enthalpy]

I should have found them earlier: patents indicate isobutene chlorination yields.

The GDR patent 106345 reacts gases to obtain 1/3 of the desired dichloro: drawing appended. Cited by the appended US pat 4587367.

The distribution of the products contradicts the radical stability: chlorinated vinyl position, no gem dichloro... Either it's baloney, or the hydrogens move often.

Starting instead with 3-chloro-2-methylpropene gives the same distribution of products, suggesting it's the first step when starting with isobutene.

The US pat 4587367 chlorinates instead with SO₂Cl₂ and a catalyst to obtain again the same distribution of products. SO₂Cl₂ is less volatile but is regenerated by guess what.

So the simplest way looks as good as the others and, despite limited yield, really cheap.

[Enthalpy]

I'm still trying to avoid the 4-days cyclopropanation towards propellane by closing 23 instead... Maybe Negishi coupling as appended  provides 23, but:

• Does Br substitute to OH rather than Cl in 20?
• Does Zn insert at Br rather than Cl?
• Does BrZnR couple with CBr₄ rather than at the chlorines of R?
• Is Zn a sensible choice, or are others (Li, Mg, B, Sn...) better, especially safer?

I had hoped to couple through HX elimination, but due to the halogens, all hydrogens seem equivalent: at CHBr₃ and the primary and the tertiary at trichlorobutane.

Thank you!
Marc Schaefer, aka Enthalpy

[Enthalpy]

No answers... Have you all lost hope for me?

[kriggy]

Heh, I just missed it.
a) I would say yes but depends on conditions http://www.organic-chemistry.org/namedreactions/appel-reaction.shtm
b) Not sure here, it works for grignards so might be the same with Zn
c) No idea but bromines are AFAIK more reactive in coupling reactions than chlorines
d) Well it depends, but I wouldnt want to work with organotlithium compounds in multitonne scalef or example if it could be avoided

[Enthalpy]

Thanks Kriggy!

Well, methyllithium is the only good path to propellane I've seen on the Web. The good side is that in 1h it's finished, but for 200t/month 24/7 the reacting amount is still about 300kg.

I wanted to avoid the 4-days-long cyclopropanation, but it looks rather harmless, and the recent alternative I suggested needs activated metals, so I doubt it's any better.

Opinions please?

[Enthalpy]

Found the selectivity of a second chlorination by Cl₂ on linear alkanes in
 35.1.1.1.2 of "Science of Synthesis" by Houben-Weyl
which tells that the gem-dichloro is half as abundent as chloros spread across the chain.

If someone knows a chlorinating agent that disfavours the gem-dichloro even more, please tell!
tBuOCl?

This makes the hypothetic alternative path of May 16, 2016 more credible (appended again, isobutene corrected).