5- Chloro pyridine, lack

Many 4-alkoxypyridines, e.g. (410), and their corresponding iV-methyl-4-alkoxypyridinium iodides (411) have been prepared and pyrolysed at temperatures less than 185 °C to give olefins derived from the alkyl moiety. The alkoxypyridines are obtained by reaction of the alkoxide with 4-chloro-pyridine. However, synthetically, the reaction suffers from a lack of stereospecificity and carbonium ion rearrangement products may be obtained. ... 

Even though data for a quantitative comparison are lacking, the effect of the position of benzo-fusion onto pyridazines is analogous to that with pyridines in producing the very poorly reactive 3-chloro-cinnoline (396) and highly reactive 1-chlorophthalazine (Table XV, lines 8 and 9). 

The N-oxide of l-pyrrolo[2,3-b]pyridine 936 is converted by the combination tri-methylsilylisothiocyanate Me3SiNCS 937/MeOCOCl to 21% 6-isothiocyanato-l-methoxycarbonyl-pyrrolo[2,3-b]pyridine 938 and 18% 6-chloro-l-methoxycarbonyl-pyrrolo[2,3-F]pyridine 939 [51] (Scheme 7.14). To avoid formation of the chloro compound 939 a reagent combination of MesSiNCS 937 with triethylamine or DBU, which lacks any competing chloride ion, might give much higher yields of... 

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