1232144-14-7Relevant articles and documents
An enantioselective claisen rearrangement catalyzed by N-heterocyclic carbenes
Kaeobamrung, Juthanat,Mahatthananchai, Jessada,Zheng, Pinguan,Bode, Jeffrey W.
supporting information; experimental part, p. 8810 - 8812 (2010/08/21)
In the presence of a chiral azolium salt (10 mol %), enols and ynals undergo a highly enantioselective annulation reaction to form enantiomerically enriched dihydropyranones via an N-heterocyclic carbene catalyzed variant of the Claisen rearrangement. Unlike other azolium-catalyzed reactions, this process requires no added base to generate the putative NHC-catalyst, and our investigations demonstrate that the counterion of the azolium salt plays a key role in the formation of the catalytically active species. Detailed kinetic studies eliminate a potential 1,4-addition as the mechanistic pathway; the observed rate law and activation parameters are consistent with a Claisen rearrangement as the rate-limiting step. This catalytic system was applied to the synthesis of enantioenriched kojic acid derivatives, a reaction of demonstrated synthetic utility for which other methods for catalytic enantioselective Claisen rearrangements have not provided a satisfactory solution.
