STEREOCHEMICAL STUDIES OF SOME 12A-SUBSTITUTED ROTENOID DERIVATIVES

The absolute configuration at 6a and 12a positions as well as the conf ormation of rings B and C or some cis fused 12a-substituted (OH, CH2OH , CH2OCOR') synthetic derivatives of natural rotenoids, rotenone and a morphigenin, are discussed on the basis of H-1 NMR, CD and molecular m echanics studies. The CD Cotton effects above 300 nm of all 12a-substi tuted derivatives, compared with those of the parent natural rotenoids , show an unexpected sign inversion and cannot be used for reliable co nfigurational assignment. This has been achieved in a nonempirical way by application of the exciton chirality method.