[darkdevil]

Hi all,
I am currently working on a pyrene derivatization reaction. The desired reaction is as follow:


The problem is, I did not get any products. Instead I obtain only the starting material pyrene, which is quite pure too.
This is what I did and some observations:
I first dissolved pyrene in anhydrous THF, and then did the lithiation with n-BuLi at low temperature. The solution quickly turned into a deep red solution. After a while, I added the benzyl chloride. The solution quickly turned into yellow and the deep red color disappeared in several seconds. I first expected that it was a sign of succeed... I then waited for about 30 minutes. and then I added water to quench the reaction (When I add water, there were no bubbles or heat evolved; and I assume there were no more carbanions within the mixture). But then when I work up my reaction mixture, did the separation with hexane and washed with water. I obtained a yellow powder and the HNMR analysis told me that I obtained my starting material pyrene !!! There were no other dirty side product peaks in the NMR spectra! ONLY pyrene!! What really happened really confuses me.
Any advice or suggestion would be greatly appreciated ! Thank you!

[Dan]

Is there precedent for this reaction in the literature? You rarely see aryllithiums participating in SN2 reactions.

You might want to consider Cu catalysis for the substitution. Another alternative is to trap your aryllithium with benzaldehyde, then a hydrogenolysis.

[clarkstill]

Yeah you'd definitely want some precedent for this... do you have a reason to expect that particular regioisomer? Also, did you use any additives in the lithiation? Generally you need tBuLi and/or TMEDA for deprotonation of not-particularly-acidic arenes in my experience.

[darkdevil]

Hi,
I found a paper doing similar things
http://www.chem.ryukoku.ac.jp/iwasawa/publications/2.%20MS_Tetrahedron%20Lett._2011_6284-6287.pdf

They mentioned they used bromopyrene and then did the lithiation and substitute with bromobutane.
I am now trying to use bromopyrene and 1) lithiate with n-BuLi and then 2) add the electrophile benzyl chloride. Nothing really happened when I added the benzyl chloride. (No color change, no signs of reactions occuring like bubbles or precipitates)

[Dan]

They mentioned they used bromopyrene and then did the lithiation and substitute with bromobutane.

They're doing Li-Hal exchange, not arene deprotonation with n-BuLi as you posted originally.

Nothing really happened when I added the benzyl chloride. (No color change, no signs of reactions occuring like bubbles or precipitates)

Visual inspection is not a great analytical method... TLC, NMR, MS?

Have you tried repeating the literature reaction with bromobutane as a positive control?

Note that the authors report reaction of the Lithiated arene with with n-BuBr produced in the Li-Hal exchange process - this will always be a competing side reaction if you use n-BuLi for the Li-Hal exchange. The authors note that it severely complicated attempted alkylation with octyl and dodecyl bromide.

I'd use BnBr, it's more reactive and should be more competitive vs the n-BuBr. Even so, expect a mess...