Chem. Pharm. Bull., 48(11),1822-1825, November 2000

Notes

Application of Rh-Catalyzed Cyclization to the Formation of a Chiral Quaternary Carbon

Miyuki TAKAHASHI, Masakazu TANAKA,* Eishi SAKAMOTO, Masanori IMAI, Kazuhisa FUNAKOSHI, Kiyoshi SAKAI, and Hiroshi SUEMUNE^*

Graduate School of Pharmaceutical Sciences, Kyushu University, Maidashi 3-1-1, Higashi-ku, Fukuoka 812-8582, Japan.

Rh-Catalyzed cyclization was applied to the formation of a chiral quaternary carbon. It has become clear that the Rh-complex can discriminate between isopropenyl and 2-isopentenyl (or isopentyl) substituents, and the cyclization afforded 3,3,4-trisubstituted cyclopentanones with a chiral quaternary carbon in a stereoselective manner. The cyclization of 4-pentenals 6a, b by an achiral neutral Rh(PPh₃)₃Cl afforded 3,3,4-cis-trisubstituted cyclopentanones (±)-7a, b in 86-96%, and the cyclization by a cationic Rh[(R)-BINAP]ClO₄ afforded 3,3,4-trans-trisubstituted cyclopentanones (-)-8a, b of 82-86% ee in 88-98% yields. The mechanism of stereoselection by Rh-complexes is also discussed.

Key words Rhodium-catalyzed cyclization; quaternary carbon; cyclopentanone; enantioselective; diastereoselective