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Radical Conjugate Addition of Nitrogen Heterocycles- A Story

March 28, 2017

In the first paper with first authors from our lab, Adam (second year graduate student) and Hengbin (postdoc) have published “A Mild Catalytic System for Radical Conjugate Addition of Nitrogen Heterocycles” in Chemical Science.

They achieved the direct addition of pyridine and diazine units to electron-poor alkenes has via a redox radical mechanism that is enabled by limiting the effective concentration of the hydrogen-atom source. The described method was found to be tolerant of acidic functional groups and is generally applicable to the union of a wide range of Michael acceptors and 6-membered heterocyclic halides. 

 

 


However, like many methodology projects, this isn't exactly what they set out to do from the start. 

Adam (best known around the lab as "Chad") was originally trying to find conditions to induce the controlled radical polymerization of ethyl acrylate upon addition of a pyridine radical. 

 

 
However, these trials gave varying degrees of polymerization in low yields. Further screening with different catalysts, solvents, electron sources and H-atom sources led to a breakthrough: Hantzsch ester (which we jokingly called Haunted Chester for months because of Google's autocorrect feature...) actually slowed the rate of polymerization down to primarily 1-2 "mers" of the polymer. 

 

 

 

From there, additional radical precursor screening, solvent screening, steric control of polymerization, limited solubility of Hantzch Ester, catalyst optimization, 400 phone calls to Agilent to fix the GC/FID and GC/MS, and one dented metal water bottle led to the paper in Chem. Sci. today.  

 

 

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