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DOI: 10.1055/s-0029-1218459
Rhodium-Catalyzed Synthesis of Pyrroles by [4+1] Cycloaddition
Contributor(s):Victor Snieckus, Emilie DavidTokyo Institute of Technology, Japan
Rhodium(I)-Catalyzed [4+1] Cycloaddition Reactions of α,β-Unsaturated Imines with Terminal Alkynes for the Preparation of Substituted Pyrrole Derivatives
Angew. Chem. Int. Ed. 2009, 48: 8318-8320
Publication History
Publication Date:
21 December 2009 (online)
Key words
cycloaddition - pyrroles - rhodium(I)
Significance
Iwasawa and co-workers report the rhodium(I)-catalyzed [4+1] cycloaddition of α,β-unsaturated imines with terminal alkynes to afford pyrrole derivatives. The best results were obtained using [{RhCl(coe)2}2] as catalyst and Cy3P as ligand. A mechanism involving nucleophilic addition of the imine nitrogen to the carbene carbon of the rhodium vinylidene complex A is proposed. In support of this mechanism, the isolated vinylidene complex {RhCl[=C=C(H)n-Hex](PCy3)2} also catalyzed the reaction under similar conditions. Further mechanistic studies have been promised.
Comment
Vinylidene complexes have been previously reported to undergo addition reactions of heteroatom nucleophiles (see Book below). The reported work describes the addition of a C=N bond to a rhodium vinylidene complex, which is not a well-documented reaction for this type of complex (A. G. M. Barrett J. Mortier, M. Sabat, M. A. Sturgess Organometallics 1988, 7, 2553; H. Fischer et al. J. Organomet. Chem. 2001, 620, 165). The reaction allows access to polysubstituted pyrroles in moderate yields and tolerates a variety of substituents.
Book: Metal Vinylidenes and Allenylidenes in Catalysis, C. Bruneau, P. H. Dixneuf, Eds.; Wiley-VCH: Weinheim, 2008.