Heterocyclcs nitrogen

PE. Evans u. A.B. Holmes, Tetrahedron 47, 9131-9166 (1991) Medium-Ring Nitrogen Heterocyclcs" (Azepines, Azocines, Azonines, and Derivatives). 

Pyridine is a rc-electron-deficient heterocyclc. Due to the electronegativity of the nitrogen atom, the a and y positions bear a partial positive charge, making the C(2), C(4), and C(6) positions prone to nucleophilic attacks. A similar trend occurs in the context of palladium chemistry. The a and y positions of halopyridines are more susceptible to the oxidative addition to Pd(0) relative to simple carbocyclic aryl halides. Even a- and y-chloropyridines are viable electrophilic substrates for Pd-catalyzed reactions under standard conditions. 

This section is concerned with methods for the ring formation of heterocyclic systems containing one, two or more hetero atoms, with the enamine nitrogen being included or not in the new heterocyclc created. 

Thymine (T) One of the four DNA biisos, a poly functional nitrogen heterocyclc. 

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