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DOI: 10.1055/s-2007-968427
Arylboron Addition-Cyclization of Cyano-Substituted Unsaturated Esters
Contributor(s):Paul Knochel, Andrei GavryushinKyoto University, Japan
Cyclization Reaction of Cyano-Substituted Unsaturated Esters Prompted by Conjugate Addition of Organoborons
Org. Lett. 2007, 9: 741-743
Publication History
Publication Date:
24 April 2007 (online)
Key words
organoboron compounds - conjugate addition - cyclization
Significance
The article describes an interesting cascade-type cyclization reaction that gives rise to useful carbocyclic enamines. This method allows the construction of new annelated five- and six-membered cycles as well as the formation of cyclic enamines from acyclic α,β-unsaturated esters. The products can be transformed into various carbo- and heterocyclic compounds. The use of chiral ligands for rhodium catalysis derives a highly enantioselective process.
Comment
The initial conjugate addition of arylrhodium(l) species to the unsaturated esters results in the (oxa-π-allyl)rhodium intermediate. Chiral ligands on Rh allow enantioselective addition similarly to the well-known Hayashi reaction. The intermediate attacks the cyano group of the molecule, and finally the enamine product is formed. In most cases, aryl-9-BBN species are preferable reagents; however, more readily available arylboronates can be used for some substrates.