Takahashi M, Tanaka M, Sakamoto E, Imai M, Funakoshi K, Sakai K, Suemune H
Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
Chem Pharm Bull (Tokyo). 2000 Nov;48(11):1822-5. doi: 10.1248/cpb.48.1822.
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]CIO4 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.
铑催化环化反应被应用于手性季碳的形成。已经明确，铑配合物能够区分异丙烯基和2-异戊烯基（或异戊基）取代基，并且该环化反应以立体选择性的方式提供了带有手性季碳的3,3,4-三取代环戊酮。非手性中性铑配合物三（三苯基膦）氯化铑催化4-戊烯醛6a、b的环化反应，以86 - 96%的产率得到3,3,4-顺式三取代环戊酮（±）-7a、b，而阳离子铑配合物[（R）-联萘二苯基膦]高氯酸铑催化该反应，则以88 - 98%的产率得到对映体过量值为82 - 86%的3,3,4-反式三取代环戊酮（-）-8a、b。同时还讨论了铑配合物的立体选择机理。
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