Asymmetric bakers yeast reductions of bridgehead-substituted bicyclo[2.2.2]octane-2,6-dione derivatives followed by conversion into catalytically active BODOLs for the diethylzinc addition to benzaldehyde
Manner S.,Kemicentrum |
Hansson C.,Kemicentrum |
Larsson J.M.,Kemicentrum |
Oltner V.T.,Kemicentrum |
Tetrahedron Asymmetry | Year: 2010
4-Substituted bicyclo[2.2.2]octane-2,6-diones have been synthesized and tested as substrates in the enantioselective reduction with bakers yeast to give the corresponding hydroxy ketones. It was found that the derivative bearing a TIPSO group at the 4-position was not reduced at all while that with a TBDMSO group gave 87% yield and 46% ee. Other 4-oxy functionalized derivatives were reduced with varying yields (36-87%) and ees (10-82%). The best result was obtained for the 4-Oallyl derivative (80% yield, 82% ee). The hydroxy ketones carrying the benzyloxy and allyloxy groups at the 4-position were converted into the corresponding BODOLs, which were tested as catalysts in the diethylzinc addition to benzaldehyde. In this reaction the ees were 90% and 89%, respectively, which showed that BODOLs substituted at the 4-position are essentially as good catalysts in this reaction as those bearing a hydrogen. © 2010 Elsevier Ltd. All rights reserved.