Asymmetric Intramolecular C-H/olefin Coupling: Rhodium-Catalyzed Asymmetric Cyclization Reactions of 1,5-Diene

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Asymmetric Intramolecular C-H/olefin Coupling: Rhodium-Catalyzed Asymmetric Cyclization Reactions of 1,5-Dienes

Fumitoshi Kakiuchi, Naoaki Fujii, Airi Yamada, Naoto Chatani, and Shinji Murai

Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565, Japan　

Recently, several examples with respect to the transition-metal catalyzed addition of C-H bonds to olefins are appeared in literature. However, there is no example for asymmetric versions. We now report on asymmetric intramolecular cyclization reactions of 1,5-dienes with the aid of a rhodium complex and a monodentate homochiral phosphine.

After various attempts for achieving asymmetric intramolecular C-H/olefin coupling reactions, the monodentate ligand (R)-(S)-PPFOMe was found to be suitable for the rhodium-catalyzed asymmetric cyclization of 1-(2-pyridyl)-1E,5Z-diene (1). The diene 1 underwent cyclization in the presence of di-m-chloro-bis[bis(cyclooctene)rhodium(I)] (5 mol%) and (R)-(S)-PPFOMe (30 mol%) in THF (0.2 M) at 120 °C (oil bath temperature) for 1 h under nitrogen to give 2 in 78% yield and 28% ee (eq 1).

Imidazole derivatives are also applicable to the present reaction. When imidazolyl diene 3 reacted, cyclized product 4 was obtained in significantly higher optical yield. In this case, the enantioselectivity was further improved by lowering the reaction temperature. The unusual mild reaction conditions for this C-H/olefin coupling reaction, i.e., at room temperature, are especially noteworthy (eq 2).

We will describe our recent progress in this area of rhodium-catalyzed intramolecular cyclizations.

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