An Enantioselective Claisen Rearrangement Catalyzed by N-Heterocyclic Carbenes

作者：Kaeobamrung Juthanat; Mahatthananchai Jessada; Zheng Pinguan; Bode Jeffrey W^*

来源：Journal of the American Chemical Society, 2010, 132(26): 8810-+.

DOI：10.1021/ja103631u

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.

• 出版日期2010-7-7