Total Synthesis of Aignopsanes, A Class of Sesquiterpenes: (+)‐Aignopsanoic Acid A, (−)‐Methyl Aignopsanoate A, and (−)‐Isoaignopsanoic A

A general strategy for the synthesis of aignopsanes, a new family of sesquiterpene natural products of marine origin, is presented. The total synthesis of (+)‐aignopsanoic acid A ( 1 ), (−)‐methyl aignopsanoate A ( 2 ), and (−)‐isoaignopsanoic A ( 3 ) has been achieved and their absolute configuration confirmed. (+)‐Microcionin‐1 ( 4 ), a structurally related furanosesquiterpene isolated in both enantiomeric forms from marine sponges, was also synthesized and its absolute configuration established in an unambiguous way. Interestingly, we report that (+)‐microcionin‐1 ( 4 ), can be converted by a simple oxidation process to aignopsanoic acid A ( 1 ). This transformation supports the hypothesis that (+)‐microcionin‐1 ( 4 ) may be an intermediate in the biosynthesis of aignopsanes.