Synthesis and Conformational Analysis of <i>N</i>-Azulenyl-<i>N</i>-methyl Amides: Influence of Coplanarity on Amide Conformational Preference

We synthesized a series of <i>N</i>-azulenyl-<i>N</i>-methylamides and investigated their conformational preferences in solution and in the solid state. <i>N</i>-(1-Azulenyl)-<i>N</i>-methyl amides <b>12</b> and <i>N</i>-(6-azulenyl)-<i>N</i>-methyl amides <b>14</b> adopt the <i>cis</i> form almost exclusively in solution and in the crystal state, like general <i>N</i>-methyl aromatic amides such as <i>N</i>-methylbenzanilide and <i>N</i>-methylacetanilide. However, <i>N</i>-(2-azulenyl)-<i>N</i>-methyl amides <b>13</b> exhibit high ratios of the <i>trans</i> form in solution and adopt the <i>trans</i> form in the solid state due to the high degree of coplanarity of the 2-azulenyl moiety and the amide plane.