Concurrent Induction of Two Chiral Centers from Symmetrical 3,4-Disubstituted and 3,3,4-Trisubstituted 4-Pentenals Using Rh-Catalyzed Asymmetric Cyclizations
journal contributionposted on 11.08.2000 by Masakazu Tanaka, Masanori Imai, Masakazu Fujio, Eishi Sakamoto, Miyuki Takahashi, Yasuko Eto-Kato, Xiao Ming Wu, Kazuhisa Funakoshi, Kiyoshi Sakai, Hiroshi Suemune
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Asymmetric cyclization of symmetrical 3,4-disubstituted and 3,3,4-trisubstituted 4-pentenals was studied using Rh-complexes with chiral ligands. The cyclization of symmetrical 4-pentenals 4a,b by a neutral Rh[(R)-BINAP]Cl afforded cis-3,4-disubstituted (4R)-cyclopentanones 9a,b of >95% ee in 25−31% yields; on the other hand, the cyclization of 4a−c by a cationic Rh[(R)-BINAP]ClO4 afforded trans-3,4-disubstituted (4S)-cyclopentanones 10a−c of >95% ee in 70−81% yields. All stereoisomers could be stereoselectively made by the selection of a neutral or cationic Rh-complex, and (R)- or (S)-BINAP ligand. The Rh-catalyzed cyclization could be applied to the construction of cyclopentanones 17 and 18 bearing a chiral quaternary carbon. The cyclization by the cationic Rh[(R)-BINAP]ClO4 afforded the optically active trans-3,3,4-trisubstituted cyclopentanones 18a−c of 92−95% ee in 75−83% yields. The catalytic cycle was also studied by using deuterium aldehyde, and the tentative mechanisms of the enantio- and diastereoselection were proposed.