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SummaryThe synthesis of 1-(2-propynyl)pyridinium salts 3 is described. Compounds 3 react with a second pyridine molecule, in the presence of the corresponding hydrochloride, to form products of type 4. Certain bases cause the 1-(2-propynyl)pyridinium salts 3 to rearrange into 1-propadienylpyridinium salts 5. Diethylamine converts compounds 3 into 1-acetonylpyridinium salts 8. Moreover, treatment of 3 or 5 with sodium methoxide gives enol ethers of type 9, which can be hydrolyzed to the ketones 8. Addition of bromine to some of the unsaturated compounds is also reported.The chemistry of 1 -vinyl-and 1-allyl-pyridinium salts has recently received more attention [l], but little is known about the 1-(1-propynyl) and 1-(2-propynyl) analogues. Reportedly, treatment of pyridine with 2-propynyl halides at 0°C for 18 h gave the 1-(2-propynyl)pyridinium halide 3f [2], while heating both reagents in a sealed tube for 15 h at 70°C [3] or 30 h at 60°C [4] afforded polymers of 1-(2-propenyl)pyridiniurn salts.We have examined the reactions of several pyridines with these halides and found a significant influence of the 4-substituent on the course of the reaction. Pyridines with a strong electron-donor substituent in the 4-position la-gave with 2-propynyl halides 2a or 2b the expected 1-(2-propynyl)pyridinium salts (3a-c) in high yields. y-Picoline (la) and 4-phenylpyridine (le), however, are much less reactive and gave 3d and 3e only in moderate yields. The 'H-NMR spectra of compounds 3a-e are characterized by a triplet near 2.8 ppm (in 3d at 2.95 ppm) and a doublet in the region 4.5-5.4 ppm due to the propynyl substituent. The coupling constants of 3 Hz agree with the expected value for a 4J coupling. The IT!-NMR spectra confirm structures 3 ( Table 1).Extending the reaction time between Id and 2b to 12 h improved the yield of 3d. However, 4-phenylpyridine (le) behaved differently. Nucleophilic attack of a second mole of 4-phenylpyridine (le) converted initially formed 3e into the pyridinium halide 4e. Compound 4e was also obtained in high yield by refluxing l e with 2-propynyl bromide (2b) in EtOH for 30 min. Treatment of pyridine If with the 2-propynyl halides 2a or 2b for 18 h either at 0°C or at 70°C gave a mixture shown spectroscopically to

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