Transition-Metal Catalysis of Triene 6π Electrocyclization: The π-Complexation Strategy Realized |
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Authors: | Pengjin Qin Li-An Wang Prof Joseph M O'Connor Prof Kim K Baldridge Yifan Li Burak Tufekci Jiyue Chen Prof Arnold L Rheingold |
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Institution: | 1. Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, 92093-0358 USA;2. School of Pharmaceutical Science and Technology, Tianjin University, 92 Weijin Road, Nankai District, Tianjin, P. R. China |
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Abstract: | Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal–alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing (C5H5)Ru(NCMe)3]PF6 as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition-metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations. |
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Keywords: | catalysis cycloaromatization electrocyclization transition metals triene |
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