Application of Rh-Catalyzed Cyclization to the Formation of a Chiral Quaternary Carbon.
作者:Miyuki TAKAHASHI、Masakazu TANAKA、Eishi SAKAMOTO、Masanori IMAI、Kazuhisa FUNAKOSHI、Kiyoshi SAKAI、Hiroshi SUEMUNE
DOI:10.1248/cpb.48.1822
日期:——
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.
铑催化的环化反应被用于形成手性四元碳。 很明显,铑络合物可以区分异丙烯基和2-异戊烯基(或异戊基)取代基,并且环化反应以立体选择性方式提供了3,3,4-三取代环戊酮,其中包含手性四元碳。 4-戊烯醛6a, b通过非手性中性铑(PPh3)3Cl的环化反应,以86-96%的收率提供了3,3,4-顺式三取代环戊酮(±)-7a, b,而通过阳离子铑[(R)-BINAP]ClO4的环化反应,以88-98%的收率提供了3,3,4-反式三取代环戊酮(-)-8a, b,其中ee为82-86%。 还讨论了铑络合物进行立体选择作用的机理。