CHEMISTRY OF PYRIDINE .8. STEROCHEMISTRY OF TETRAHYDROPYRIDINES ISOLATED FROM REACTION OF PYRIDINE N-OXIDES WITH MERCAPTANS IN ACETIC ANHYDRIDE

The complexity of the 100-MHz spectra of five 1-acetyl-2-acetoxy-3,6-(dialkylmercapto)-1,2,3,6-tetrahydropyridines produced from the reaction of pyridine, 4-picoline, and 4-phenyl- and 4-t-butylpyridine 1-oxides with mercaptans in acetic anhydride3 is attributed to restricted rotation of the N-acetyl group. It was possible to obtain pmr parameters associated with two rotamers in solution. The α ring protons in these N-acetylpiperideines exhibited the greatest chemical-shift differences, of the order of 1 ppm. The pmr spectra also substantiated the structures of 1-acetyl-2,3,6-tri-t-butylmercapto-4-t-butyl-1,2,3,6-tetrahydropyridine and 1-acetyl-2,6-diacetoxy-3,5-dimethyl-3-t-butylmercapto-1,2,3,6-tetrahydropyridine, which had been isolated previously. An interesting chemical-shift difference for a methine proton was observed (~1.5 ppm downfield) in two of the above compounds, when only part of their structure was changed from -CH(SR)CH(SR)- to -CH(SR)CH(OAc)-. © 1969, American Chemical Society. All rights reserved.