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Download fileDomino Cyclization of 1,n‑Enynes (n = 7, 8, 9) Giving Derivatives of Pyrane, Chromene, Fluorene, Phenanthrene and Dibenzo[7]annulene by Ruthenium Complexes
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posted on 2016-04-30, 00:00 authored by Hao-Wei Ma, Pei-Min Chen, Ji-Xian Lo, Ying-Chih Lin, Shou-Ling Huang, Chi-Ren Chen, Pi-Yeh ChiaCyclization of the ether enyne 1 catalyzed by [Ru]NCCH3+ ([Ru] = Cp(PPh3)2Ru) in
CHCl3 generates a diastereomeric mixture of the substituted
tetrahydropyran 11. Presumably, formation of an allenylidene
complex is followed by a cyclization by nucleophilic addition of the
olefinic group to Cγ of the ligand giving a boat-like six-membered
ring. The diastereoselectivity is controlled by the 1,3-diaxial interaction.
The vinylidene complex 7, a precursor of 11, is obtained from 1 and [Ru]Cl. In a mixture of MeOH/CHCl3, the domino cyclization of 1 further affords 14a, a chromene product catalytically. The second cyclization
proceeds via nucleophilic addition of the resulting olefinic unit
to Cα of 7. But the ether enyne 3 with
a cyclopentyl ring on the olefinic unit undergoes only single cyclization
due to steric effect. The propargyl alcohol and the two terminal methyl
groups on the olefinic unit shape the cyclization. Thus, similar all-carbon
1,n-enynes (n = 7, 8, 9) 4–6 each with an aromatic linker undergo direct
domino cyclization catalyzed by [Ru]NCCH3+,
to give derivatives of tricyclic fluorene, phenanthrene and dibenzo[7]annulene,
respectively, with no intermediate observed.