First Enantiospecific Total Synthesis of the Antitubercular Marine Natural Product Pseudopteroxazole. Revision of Assigned Stereochemistry

A concise, enantiospecific synthesis of pseudopteroxazole (3), which had originally been assigned structure 1, has been accomplished starting from S-(-)-limonene. The known cyclohexanone 5 was converted in five steps to the alpha,beta-enone 8 by a modified Robinson annulation. Transformation of 8 to the orthogonally protected amino phenol 11 was accomplished by a new modification of the Wolff-Semmler rearrangement. The synthesis was completed by cationic cyclization to form 14 diastereoselectively and subsequent introduction of the terminal oxazole subunit.