Organocatalytic Asymmetric Claisen Rearrangement

Abstract

Catalysis of the Claisen rearrangement by simple guanidinium salts such as N,N′-diphenylguanidinium salt 1 is reported. A broad variety of substituted allyl vinyl ethers (see selected examples) were suitable substrates for this interesting transformation. Moreover, highly enan­tioselective Claisen rearrangements of ester-substituted allyl vinyl ethers 2 have been achieved using C 2-symmetric guanidinium salt 3 as the catalyst. Other types of substrates failed to give satisfying results in the asymmetric variant. The weakly coordinating counterion BArF- was found to be crucial for catalytic activity of the respective guanidinium salt.