Enantiospecific Total Synthesis of (−)-4-Thiocyanatoneopupukeanane<sup>†</sup>

2001-05-22T00:00:00Z (GMT) by A. Srikrishna Santosh J. Gharpure
Enantiospecific synthesis of the natural enantiomer of the marine sesquiterpene (−)-4-thiocyanatoneopupukeanane (<b>6</b>) is described. The bicyclo[2.2.2]octanecarboxylate <b>14</b>, obtained from (<i>R</i>)-carvone via Michael−Michael reaction, was transformed into neopupukeananedione <b>12</b> by employing rhodium acetate catalyzed intramolecular C−H insertion of the diazo ketones <b>16</b> or <b>19</b> as the key reaction. Regioselective deoxygenation of the C-2 ketone transformed the dione <b>12</b> into neopupukean-4-one <b>10</b>. Alternately, the keto ester <b>18</b> was also transformed into neopupukean-4-one <b>10</b> via regioselective deoxygenation of the ketone in <b>18</b> followed by intramolecular rhodium carbenoid C−H insertion of the diazo ketone <b>31</b>. Finally, neopupukean-4-one <b>10</b> was transformed into (−)-4-thiocyanatoneopupukeanane <b>6</b> via the alcohol <b>32</b> and the mesylate <b>33</b>.