Grignard allylic substitution catalyzed by imidazol-2-ylideneand

概要

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In the presence of a catalytic amount of 1,2-disubstituted or 1,2,3-trisubstituted imidazolium salts, γ-substituted allyl chlorides reacted with alkyl Grignard reagents to undergo substitution reactions in an SN2′-selective fashion, where the magnesium ate complexes [(N-heterocyclic carbene-MgR3)−(MgX)+] of imidazol-2-ylidenes or imidazol-4-ylidenes, generated in situ, were postulated as the active species. It was observed that the reactions with imidazol-4-ylidene catalysts were faster than those with imidazol-2-ylidenes. Enantioselective catalysis using a chiral imidazolium salt was preliminarily investigated.
2010-10-27