I remember at one point having a (review?) paper called “Pyridine!” in my collection. Love that title. I can’t remember who wrote it, what year it was from or what it contained. Now I can’t find it again, because SciFinder and Google Scholar seem to ignore the exclamation mark in text based searches. If you know of a workaround or how else to rediscover this article, please tell me.
Anyways, pyridines and pyridones lie close to my heart, and I am delighted to see the latest progress in synthesis of highly substituted pyridines. I think it was Manfred Schlosser, the crowned King of pyridines, who coined the term “regioexhaustive functionalizations”, which I try to reuse as often as possible.
During this fall in Organic Letters alone there appear at least three excellent papers on the topic.
Org. Lett. 2011, 13, 5394–5397. (DOI: 10.1021/ol202290y)
Org. Lett., Article ASAP (DOI: 10.1021/ol202691b)
Org. Lett., Article ASAP (DOI: 10.1021/ol202679t)
Normally, I would paste the graphical abstracts here, but as time is not on my side right now, you will have to suffice with uncovering these manually – this time only. I can however vouch for the awesomeness of all three, if you are at all into heterocyclic chemistry.
Finally, I would like reveal my hidden agenda and turn your attention and this post into a blatant plug for one of our own publications. Ha! We were the first to synthesize pyridines substituted with five different elements (1 and 2).
Synthesis 2010, 63-66. (DOI: 10.1055/s-0029-1217084).
What we did not realize until the paper had been accepted and proofed was that we missed a golden opportunity to introduce a sixth element. Do you see it?
Upon treatment of pyridine 2 with MCPBA, you would get a pyridine substituted with six different elements, the N-oxide, right? Any takers? (Please mention us when you publish.)
the treatment of pyridine 2 with m-CPBA you will get you sulfoxide and then immediately the sulfone. You would have to beat much harder on it to get it all the way to N-oxide-sulfone.
There is a lovely preparation where you oxidize 2-methylthio-4,6-dichloropyrimidine with mCPBA to the Me-sulfone (without harming the ring nitrogens and then you displace the produced methylsulfone in 2-position with a (poorly reactive) amine under mild conditions, this substitution leaves the two chlorines unmolested.
also there is a risk that N-oxidation attempt would produce desilylated products, possibly 2-hydroxypyridine too.
Do you think I would post the perfect recipe just like that? 🙂
You’re right, of course. MCPBA is a poor choice. But… I can’t think of anything right now that would prefer N over S.