Asymmetric Total Syntheses of Di‐ and Sesquiterpenoids by Catalytic C−C Activation of Cyclopentanones

Abstract

To show the synthetic utility of the catalytic C−C activation of less strained substrates, described here are the collective and concise syntheses of the natural products (−)‐microthecaline A, (−)‐leubehanol, (+)‐pseudopteroxazole, (+)‐seco‐pseudopteroxazole, pseudopterosin A–F and G—J aglycones, and (+)‐heritonin. The key step in these syntheses involve a Rh‐catalyzed C−C/C−H activation cascade of 3‐arylcyclopentanones, which provides a rapid and enantioselective route to access the polysubstituted tetrahydronaphthalene cores presented in these natural products. Other important features include 1) the direct C−H amination of the tetralone substrate in the synthesis of (−)‐microthecaline A, 2) the use of phosphoric acid to enhance efficiency and regioselectivity for problematic cyclopentanone substrates in the C−C activation reactions, and 3) the direct conversion of serrulatane into amphilectane diterpenes by an allylic cyclodehydrogenation coupling.