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February 19, 2013
More From Blog Syn
I wanted to mention that there are two more entries up on Blog Syn: one of them covering this paper on alkenylation of pyridines. (It's sort of like a Heck reaction, only you don't have to have an iodo or triflate on the pyridine; it just goes right into the CH bond). The short answer: the reaction works, but there are variables that seem crucial for its success that were under-reported in the original paper (and have been supplied, in part, by responses from the original author to the Blog Syn post). Anyone thinking about running this reaction definitely needs to be aware of this information.
The latest is a re-evaluation of a older paper on the use of IBX to (among many other things) oxidize arylmethane centers. It's notable for a couple of reasons: it's been claimed that this particular reaction completely fails across multiple substrates, and the reaction itself is from the Nicolau lab (with Phil Baran as a co-author). Here's the current literature situation:
A day in the library can save you a week in the lab, so let’s examine this paper’s impact using SciFinder: it's been cited 179 times from 2002-2013. Using the “Get Reactions" tool, coupled with SciFinder’s convenient new “Group by Transformation” feature, we identified 54 reactions from the citing articles that can be classified as “Oxidations of Arylmethanes to Aldehydes/Ketones" (the original reaction's designation). Of these 54 reactions, only four (4) use the conditions reported in this paper, and all four of those come from one article: Binder, J. T.; Kirsch, S. F. Org. Lett. 2006, 8, 2151–2153, which describes IBX as “an excellent reagent for the selective oxidation to generate synthetically useful 5-formylpyrroles.” Kirsch's yields range from 53-79% for relatively complex substrates, not too shabby.
I'll send you over to Blog Syn for the further details, but let's just say that not many NMR peaks are being observed around 10 ppm. Phil Baran himself makes an appearance with more details about his recollection of the work (to his credit). Several issues remain, well, unresolved. (If any readers here have ever tried the reaction, or have experience with IBX in general, I'm sure comments would be very welcome over there as well).
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