The'H NMR spectrum of 22 shows the protons of tert-butyl groups as two different singlets at 1.13 and 1.23 ppm, while the olefinic protons give two doublets at 6.14 (J= 2 Hz) and 6.93 (J= 2 Hz) ppm. On the basis of the NMR spectral data, asymmetric structures 24a and 24b can be omitted from the possible structures. yfyv Cl c1