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DOI: 10.1055/s-0029-1220005
Organocatalytic Carbocyclizations
Rezensent(en):Benjamin List, Ilija ČorićPrinceton University, USA and Harvard University, Cambridge, USA
Enantioselective Polyene Cyclization via Organo-SOMO Catalysis
Enantioselective Thiourea-Catalyzed Cationic Polycyclizations
J. Am. Chem. Soc. 2010, 132: 5027-5029; J. Am. Chem. Soc. 2010, 132: 5030-5032
Publikationsverlauf
Publikationsdatum:
20. Mai 2010 (online)
Key words
polyene cyclization - cationic polycyclization - organo-SOMO catalysis - thiourea catalysis
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Significance
The research groups of MacMillan and Jacobsen have developed examples of organocatalytic carbocyclizations. Rendler and MacMillan employed organo-SOMO catalysis for cyclizations of polyene aldehydes (e.g., 3). Polycycles (e.g., 4) were obtained in good yields and enantioselectivity with 30 mol% of secondary amine catalyst 1. Jacobsen and co-workers developed thiourea catalyst 2 which effects polycyclization of hydroxylactams (e.g., 5). Polycycles (e.g., 6) were obtained in moderate to good yields and enantiomeric ratios up to 97:3.
Comment
The biosynthesis of complex cyclic terpenes from polyene precursors has inspired the development of biomimetic polyene cyclizations (R. A. Yoder, J. N. Johnston Chem. Rev. 2005, 105, 4730). An enantioselective polyene cyclization induced by Lewis acid assisted chiral Brønsted acid has been developed recently (H. Ishibashi, K. Ishihara, H. Yamamoto J. Am. Chem. Soc. 2004, 126, 11122). The cationic polycyclization reported by Jacobsen is initiated by the formation of a catalyst-bound iminium-chloride ion pair. As the enantioselectivity of the reaction is highly dependent on the size of the arene substituent in 2, stabilizing cation-π-interactions were proposed. Rendler and MacMillan have accomplished radical polycyclization of polyenals using the previously established organo-SOMO catalysis concept.
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