Enantio- and diastereoselective construction of 4,9-dimethylspiro[4.4]nonane-2,7-dione using Rh-catalyzed asymmetric cyclization

Asymmetric cyclization using Rh-complexes was applied to the synthesis of 4 ,9-dimethylspiro[4.4]nonane-2,7-diones. The spiro[4.4]nonane skeleton beari ng a chiral quaternary carbon could be stepwisely constructed by using Rh-c atalyzed cyclization twice. All diastereomers of the spirodiketone could be stereoselectively prepared from the identical starting material by the com bination of a neutral Rh(PPh3)(3)Cl and a cationic Rh[BINAP]ClO4. The cycli zation by the neutral Rh(PPh3)(3)Cl proceeded to give cis-3,4-disubstituted cyclopentanones, while that by the cationic Rh[BINAP]ClO4 proceeded to aff ord trans-3,4-disubstituted cyclopentanones. Four spirodiketones of six ste reoisomers could be prepared in optically active form, and the relationship between the stereochemistry of the spirodiketones and the Rh-complex was d iscussed based on the plausible acyl-hydride Rh-complexes. (C) 2001 Elsevie r Science Ltd. All rights reserved.