Boger pyridine synthesis

Pyridine synthesis via hetero-Diels-Alder reaction of 1,2,4-triazines and dieno-philes (e.g. enamine) followed by extrusion of N2. 

Dale Boger is a professor at the Scripps Research Institute. 

Galatsis, P. Boger Reaction In Name Reactions in Heterocyclic Chemistry, Li, J. J. Corey, E. J. Eds. Wiley Sons Hoboken, NJ, 2005, 323-339. (Review). 

Name Reactions A Collection of Detailed Mechanisms and Synthetic Applications, DOI 10.1007/978-3-319-03979-4 31, Springer International Publishing Switzerland 2014 

2179-2182. Dale Boger obtained his Ph.D. under E.J. Corey at Harvard University in 1980. He started his independent career at the University of Kansas, moving onto Purdue University, and currently he is a professor at The Scripps Research Institute. 

Reduction (often using NaCNBHs) of an imine, formed by condensation of an amine and a carbonyl, to afford the corresponding amine. 

Name Reactions, 4th ed., DOI 10.1007/978-3-642-01053-8 27, Springer-Verlag Berlin Heidelberg 2009 

Lawecka, J. Bujnicki, B. Drabowicz, J. Rykowski, A. Tetrahedron Lett. 2008,49, 719-722. 

---

The Boger pyridine synthesis involves the reaction of triazine 1 with activated alkene 2 in a hetero-Diels-Alder fashion. The intermediate bicyclic species 3 is unstable and a facile cycloreversion takes place due to the loss of nitrogen gas to afford the appropriately substituted pyridine derivative 4. 

Applieation of this theory to the Boger pyridine synthesis reveals that it is a LUMOdiene-controlled Diels-Alder reaetion. Sinee the 1,2,4-triazine is eleetron defieient as a result of the ring nitrogen atoms, one must pair this diene with eleetron rieh dienophiles to allow optimal HOMO-LUMO pairing for this reaetion to beeome faeile. 

The Boger pyridine synthesis involves an inverse-electron demand hetero-Diels-Alder [4 + 2] reaction of the electron-deficient 1,2,4-triazine... 

Example 2, Similar to the Boger pyridine synthesis (see page 59) ... 

---