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15.1.1.4.4.2.4 Method 4: Addition–Elimination Reactions

DOI: 10.1055/sos-SD-015-00002

Spitzner, D.Science of Synthesis, (200515193.

Addition of nucleophiles to pyridine 1-oxides occurs preferentially at position 2. Both allyltrimethylsilane and trimethylsilyl cyanide (also prepared in situ) add to pyridine 1-oxide (802) to give the corresponding 2-substituted pyridines, 818 and 819 (Scheme 271).[‌1044‌,‌1045‌] 1,4-Addition [formation of pyridine-4-carbonitrile (820)] is not observed under these conditions. Stronger activation is achieved by alkylation or acylation (e.g., with benzoyl chloride or dimethylcarbamyl chloride) of the pyridine 1-oxide to give the corresponding pyridinium salt which reacts easily with a variety of nucleophiles.[‌1046‌‌1053‌] The intermediate acylpyridinium salt formation followed by the additionelimination reaction is performed in one pot.[‌1054‌] Silver salts of alkynes add in modest yields (2050%) to such activated pyridine 1-oxides.[‌1038‌]

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