Schafroth MA, Sarlah D, Krautwald S, Carreira EM * ETH Zürich, Switzerland
Iridium-Catalyzed Enantioselective Polyene Cyclization.
J. Am. Chem. Soc. 2012;
134: 20276−20278
Key words
polycyclization - iridium - zinc triflate - polyenes
Significance
The biogenic isoprene rule, established in 1955 by Ruzicka, Eschenmoser, and Stork (Helv. Chim. Acta 1955, 38, 1890; J. Am. Chem. Soc. 1955, 77, 5068), stimulated biomimetic studies for the construction of polycyclic frameworks, like the steroid skeleton. Approaches based on Brønsted/Lewis acid catalysis (Yamamoto, Loh, Corey), organocatalysis (Ishihara, MacMillan, Jacobsen), and transition-metal catalysis (Takeuchi, Helmchen, Hartwig) are reported.
Comment
The authors report the development of a highly enantioselective polycyclization method using the combination of Lewis acid activation with iridium-catalyzed allylic substitution. This strategy relies on direct use of branched, racemic allylic alcohols and furnishes a diverse and unique set of carbo- and heteropolycyclic ring systems in good yield and ≥99% ee.
