Organocatalytic Ring Construction The Corey Synthesis of Coraxeniolide

Oiganocatalysts can also be used to prepare polycyclic systems. Professor Jorgensen has found (Chem. Commun. 2008, 3016) that condensation of 14 with acetone dicarboxylate 17, again using catalyst 3a, gave the bicyclic P-keto ester 18. Matthew J. Gaunt of the University of Cambridge observed (J. Am. Chem. Soc. 2008,130,404) that for the cycliza-tion of 19, catalyst 3b was superior to catalyst 3a. The power of desymmetrization of prochiral intermediates was illustrated by the report (J. Am. Chem. Soc. 2008,130, 6737) from Benjamin List of the Max-Planck-lnstitute, Mulheim of the cyclization of 21 to 23. 

Damien Bonne and Jean Rodriguez of Aix-Marseille Universite employed (Organic Lett. 2008, 10, 5409) intramolecular dipolar cycloaddition to convert the initial adduct between 22 and 23 to the cyclopentane 24. They also prepared cyclohexane derivatives using this approach. 

The most powerful such Robinson annulation reported to date was by (Organic Lett. 2008, 10, 3753) Karl Anker Jorgensen of Aarhus University, Denmark, who showed that a-alkyl acetoacetates such as 32 could be combined with the silyl aldehyde 33 to give the 5-silyl cyclohexenones 34. Conjugate addition to such cyclohexenones is expected to proceed with high diastereocontrol, leading, for instance, after oxidative desilylation to the 5,6-dialkyl cyclohexenone. 

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Organocatalytic Ring Construction The Corey Synthesis of Coraxeniolide A... 

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