Abstract
By separation of the enantiomers of the woody-ambery odorant 10-acetyl-9,10-dimethylbicyclo[6.4.0]dodec-1(8)-ene (rac-12) via their diastereomeric (-)-camphanoates, the (-)-(9R,10S)-isomer (9R,10S)-12 was determined to be the most powerful enantiomer. With an odor threshold of 0.19 ng/L it is about one hundred times stronger than its antipode. Racemic 10-acetyl-9,10-dimethylbicyclo[6.4.0]dodec-1(8)-ene (rac-12) was synthesized by an unusual [4+2]-cycloaddition of 4-methylenespiro[2.7]decane (10) and 3-methylbut-3-en-2-one (11) in the presence of Wilkinson’s catalyst. However, attempts to induce optical activity with chiral rhodium(I) catalysts proved futile. Platinum(II)-DIOP catalysts furnished traces (0.05% GC yield) of (-)-(9R,10S)-10-acetyl-9,10-dimethylbicyclo[6.4.0]dodec-1(8)-ene [(9R,10S)-12] with an enantiomeric excess of around 40% ee. For further studies on the structure-odor correlation of woody odorants, two new tricyclic analogs of rac-12, (±)-(2R*,3S*,7S*)-2-methyltricyclo[7.6.0.03,7]pentadec-1(9)-en-4-one (18) and (±)-(2R*,3S*,7S*)-2,3-dimethyl-tricyclo[7.6.0.03,7]pentadec-1(9)-en-4-one (20) were synthesized and characterized.
Key words
catalysis - cycloadditions - enantiomeric resolution - odorants - polycycles
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14 Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supple-mentary publication no. CCDC-217321, CCDC-218099, and CCDC-219739. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: +44(1223)336033;
E-mail: deposit@ccdc.cam.ac.uk].
