Total Syntheses of (−)-Mersicarpine, (−)-Scholarisine G, (+)-Melodinine E, (−)-Leuconoxine, (−)-Leuconolam, (−)-Leuconodine A, (+)-Leuconodine F, and (−)-Leuconodine C: Self-Induced Diastereomeric Anisochronism (SIDA) Phenomenon for Scholarisine G and Leuconodines A and C

Enantioselective total syntheses of title natural products from a common cyclohexenone derivative (<i>S</i>)-<b>18</b> were reported. Ozonolysis of (<i>S</i>)-<b>18</b> afforded a stable diketo ester (<i>R</i>)-<b>17</b> that was subsequently converted to two skeletally different natural products, i.e., (−)-mersicarpine (<b>8</b>) with a [6.5.6.7] fused tetracyclic ring system and (−)-scholarisine G (<b>9</b>) with a [6.5.6.6.5] fused pentacyclic skeleton, respectively. The postcyclization diversification was realized by taking advantage of the facile conversion of (+)-melodinine E (<b>6</b>) to <i>N</i>-acyliminium ion <b>7</b>, from which a hydroxy group was selectively introduced to the C6, C7, C10 and the central C21 position of diazafenestrane system, leading to (−)-leuconodine A (<b>11</b>), (+)-leuconodine F (<b>12</b>), (−)-scholarisine G (<b>9</b>), (−)-leuconodine C (<b>13</b>), and skeletally different (−)-leuconolam (<b>5</b>). Furthermore, an unprecedented non-natural oxabridged oxadiazafenestrane <b>68</b> was formed by oxidation of (+)-melodinine E (<b>6</b>). During the course of this study, a strong self-induced diastereomeric anisochronism (SIDA) phenomenon was observed for scholarisine G (<b>9</b>), leuconodines A (<b>11</b>) and C (<b>13</b>). X-ray structures of both the racemic and the enantiopure natural products <b>9</b>, <b>11</b>, and <b>13</b> were obtained. The different crystal packing of these two forms nicely explained the chemical shift differences observed in the ¹H NMR spectra of the racemic and the enantio-enriched compounds in an achiral environment