Abstract: “This project describes a site-selective functionalization of an alkenyl C-H bond using a modified Catellani reaction. The Catellani reaction, catalyzed by palladium and norbornene, traditionally results in both ortho and ipso functionalization of an aromatic ring. However, the corresponding alkenyl C-H functionalization via Pd/norbornene dual catalysis remains rare. On the other hand, Pd(II)-catalyzed directed C-H activation is well established through the formation of a palladacycle intermediate. This strategy relies heavily on substrate design and typically only activates the proximal C-H bond. In order to mediate these limitations, we report a catalyst-controlled distal alkenyl C-H functionalization. The reaction conditions are fairly mild and the time span of the reaction is only twelve hours. A variety of functional groups were shown to be compatible with the reaction conditions. In addition, both cyclic and linear alkenes reacted to form the desired product in a high yield. Mechanistic studies demonstrated that the reaction mechanism is consistent with that of the proposed Catellani reaction. Ultimately, the reported reaction is one of the first reactions in which the Catellani reaction can be applied to an alkenyl C-H bond to result in a distal C-H bond functionalization, providing a new and elegant synthetic tool.”
East Central IL ACS Undergraduate Research Conference
Thank you for joining us for the 5th Annual ECI-ACS conference!
Hi Nina, great presentation! Your aryl substrate scope is very electron withdrawing. I was wondering, have you been able to show any electron neutral or electron rich aryl groups for this reaction? If not, why do you think that is the case? Thanks!
Hi Rachel, thanks for your comment! We were able to show some examples of slightly electron-rich aryl iodides, such as 3o and 3p, with a decently high reactivity. However, these tend to be somewhat less reactive, as our aryl iodide is functioning as an electrophile. In addition, having an electron-withdrawing group ortho to the iodide improved reactivity, most likely by helping facilitate the oxidative addition between the aryl iodide and the palladacycle.
Great presentation! Really enjoyed hearing about your work. I have a question about the directing group. Throughout the presentation you have the directing group on an oxygen, but then on the last slide you show an example where you have a directing group on a nitrogen. Can you use nitrogen, oxygen, and potentially other functional groups interchangeably for the directing group?
Hi Shelby, thanks for your comment! There are many different types of directing groups. In our case, the oxime ether type directing group bonded to an oxygen worked best for most of our substrates. However, we did screen a number of other directing groups, including the one shown on the last slide. Typically, the directing group will contain an O or an N to coordinate with palladium. I’ve seen examples of pyridine-based directing groups, and even transient directing groups derived from CO2.
Hello Nina!
Very nice and clear presentation!
Why do you think that DG1 worked the best out of the different directing groups that you tried?
Hi Tiffany,
Thank you for your comment!
We aren’t entirely sure why DG1 worked so well compared to the other directing groups. It’s a bit like the norbornene substituents – we know that different substituents affect reactivity, but we aren’t totally sure how. DG3 is derived from an aldehyde. These directing groups tend to work well with an sp3-hybridized C-H activation, but weren’t very useful for our sp2-hybridized system.