Asymmetric reactions Claisen-Cope rearrangement

The tandem Cope Claisen reaction of substrate 8 yields a 22 78 mixture of aldehydes 10 and 11. The initial Cope rearrangement proceeds exclusively through the chairlike transition state. The Claisen step results from the relative asymmetric induction exhibited by the ring substituent with preferred irans-C —C bond formation. The major diastereomer 11 has been transformed into the pseudoguaianolide aromatin399,400 1165. 

Allyl aryl ethers undergo accelerated Claisen and [1,3] rearrangements in the presence of a mixture of trialkylalanes and water or aluminoxanes. The addition of stoichiometric quantities of water accelerates both the tiimethylaluminum-mediated aromatic Claisen reaction and the chiral zirconocene-catalyzed asymmetric carboalumination of terminal alkenes. These two reactions occur in tandem and, after oxidative quenching of the intermediate tiialkylalane, result in the selective formation of two new C-C bonds and one C-0 bond (Eq. 12.70). Antibodies have also been developed to catalyze Claisen " and oxy-Cope rearrangements. 

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