Pyridine effect

S. Goldmann and J. Stoltefuss, 1,4-Dihydro-pyridines effect of chirality and conformation on the calcium-antagonistic and -agonistic effects, Angew. Chem. 1991, 103, 1587-605 Angew. Chem. Int. Ed. En. 1991, 30, 1559-1578. 

The Doebner-Modification in refluxing pyridine effects concerted decarboxylation and elimination ... 

Pyridine effectively stabilizes the short-lived organic carbenes 36 by forming the corresponding pyridinium ylides 37 that are far more stable than the starting carbene (Equation 14). 

In pyrrol-2-yl-pyridines, effective 7t,7t-conjugation between the pyrrole and pyridine cycles takes place, the former being a re-donor (00RJO1074). A noticeable transmittance of the COCF3 electronic effect through the pyrrole moiety to the pyridine cycle was observed. For 3-(pyrrol-2-yl)pyridine, syn- and AMfi-conformations were registered, while for 2-(pyrrol-2-yl)pyridine only syM-conformation, stabilized by the intramolecular NH N bond, was detectable. 

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