Determination of the gauche effect of 3-acetamido- and 3-acetoxy-piperidine and -tetrahydropyran by 1H-n.m.r. spectroscopy

Article abstract of DOI:10.1016/0008-6215(90)84017-O

The A-values of the acetamido and the acetoxy group were determined by low-temperature 1H-n.m.r. spectroscopy.The limiting values for the relevant vicinal coupling constants of the newly prepared trans- (22) and cis-5-acetoxy-2-(1-hydroxy-1-methylethyl)tetrahydropyran (24) were obtained at room temperature.The attractive gauche effect of AcNH-3 and AcO-3 in piperidines, piperidinium trifluoroacetates, and tetrahydropyrans was investigated by 1H-n.m.r. spectroscopy both at low temperature (integrals) and at room temperature (band widths and coupling constants).The results obtained at low temperature are more reliable.The position of the conformational equilibrium of N-(3-piperidyl)acetamide (11), N-(1-methyl-3-piperidyl)acetamide (12), and N-(tetrahydropyran-3-yl)acetamide (17) depends strongly upon the nature of the solvent and, in apolar solvents, upon the concentration.