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Diketone 5 has already been prepared from 3 by epoxidation followed by MeONa treatment, but the yield of 5 was only 8.3 %.

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All new compounds have been satisfactorily characterized by IR, ¹H NMR (60 or 400 MHz) and high resolution mass spectrometry (or elemental analysis).

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The stereostructure of 8 was deduced as 8-A by ¹H NMR (400 MHz) analysis. This assignment was confirmed by conversion into 2 as described later. ¹H-NMR(CDCl₃ 400 MHz) 8: δ 1.09, 1.12, 1.40 and 3.70 (each s, Me), 1.14 (d, J= 7.6 Hz, 8α-Me), 2.30 (10β-H), 2.57 (8β-H), 2.61 (1β-H), 2.96 (10α-H), 3.9-4.0) (m, 4H). By-product 9 is considered to be a stereoisomer of 8 from¹NMR data, but its stereostructure is remained unknown.

Even if epimerization takes place during conversion of 6 into 7, the resulting ii having a quassi-ax CO₂Me group may be flipped Into a more stable i having a quassi-eq CO₂Me group, which is an enantiomer of ii having a quassi-eq CO₂Me group.

The corresponding Δ⁹-isomer was not detected in this reaction.

¹H NMR (CDCl₃) 14a(less polar gum): δ 0.89, 1.36 and 3.23 (each s. Me), 1.13 (d, J= 6.7 Hz, Me), 1.54 (d, J= 1.7 Hz, Me), 14b(more polar gum): δ 0.79 and 0.92 (each s. Me), 1.08 (d, J= 6.5 Hz, Me), 1.65 (d, J= 1.5 Hz, Me), 3.15 (s, 2.5H), 3.42 (s, 0.5H).

Compounds b₁, b₂ are stereoisomers due to sulfoxide moiety. ¹H NMR(CDCl₃) 15a(86 %): δ 0.99, 1.23 and 3.37 (each s. Me), 1.16 (d, J= 6.7 Hz, Me), 1.55 (d, J= 1.9 Hz, Me). 15b₁(less polar, 61 %): δ 0.86, 1.02 and 3.15 (each s. Me), 1.07 (d, J= 6.5 Hz, Me), 1.62 (d, J= 1.4 Hz, Me). 15b₂(more polar, 27 %): δ 1.00, 1.51 and 3.40 (each s. Me), 1.19 (d, J= 6.7 Hz, Me), 1.68 (d, 3= 1.2 Hz, Me).

2a (less polar oil, 53.5 %): ¹H NMR CDCl₃) δ 0.96 (d, J= 6.8 Hz, 4-Me), 0.98 and 1.18 (each s, 11α- and 11β-Me), 1.62 (d, J= 1.6 Hz, 8-Me), 5.25– 5.55 (m, 9-H). IR(CCl₄) 1720(sh), 1695 cm⁻¹, High resolution MS(m/z) Calcd for C₁₅H₂₄O(M⁺): 220.1826, Found: 220.1837. 2b (more polar oil, 32 %): ¹H NMR(CDCl₃) δ 0.97 and 1.15 (each s, 11α and 11β-Me), 1.04 (d, J= 7 Hz, 4-Me), 1.64 (d, J= 1.7 Hz, 8-Me), 5.15– 5.45 (m, 9-H), IR(CCl₄) 1735(sh), 1685 cm⁻¹. High resolution MS(m/z) Found: 220.1820.