I understand step A involves reductive ozonolysis. and that step B is addition involves addition of ammonia to the carbonyl site to form imines. But what does the sodium salt of trichloroacetic acid do? I'm inclined to say C or D since I cannot explain how else the extra double bonds form with a strong slant towards C because I would expect di-chlorination for D.
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1$\begingroup$ It doesn't look like a common reaction, indeed. I think you're right about the first step. As for the second step, OK, let's say that you formed an imine with one carbonyl. What happens then? As for the last step, I think it's like the carbene reaction described here: books.google.be/… $\endgroup$– user6376297Apr 16, 2019 at 17:00
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$\begingroup$ I do know the carbene mechanism but it doesn't seem how even the dichloro carbene is generated! I am also familiar with the abnormal reimer teimann reaction $\endgroup$– Aditya GargApr 16, 2019 at 17:25
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1$\begingroup$ Here is a report on decomposition of sodium trichloroacetate in the presence of amines: pubs.acs.org/doi/abs/10.1021/jo01050a541?journalCode=joceah $\endgroup$– Karsten ♦Apr 16, 2019 at 17:50
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$\begingroup$ Here is another one: onlinelibrary.wiley.com/doi/abs/10.1002/recl.19610800707. If it does not help you directly, it might help someone else to write an answer. Both papers establish that under the right conditions, sodium trichloroacetate decomposes to form dichloro carbene, CO2 and sodium chloride. (I'm not at the level to understand them either...) $\endgroup$– Karsten ♦Apr 16, 2019 at 18:00
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1 Answer
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Step 1 is ozonolysis with reductive work-up giving butan-1,4-dialdehyde. Step 2 reaction with NH3 gives pyrrole. Step 3 is the interesting one. As the discussion in the comments states the thermal decomposition of sodium trichloroacetate gives dichlorocarbene. This adds to one of the double bonds of pyrrole to give initially the dichlorocyclopropane. This is unstable and rearranges to give 3-Chloropyridine. This gives higher yields in neutral aprotic solvents reference here. Further discussion and mechanism here
Image from reference 2
answered Apr 16, 2019 at 18:28