Cadinane synthesis

The structures of notonipetrone (185) ° and the two abrotanifolone derivatives (186) and (187) have been deduced on the basis of n.m.r. spectral evidence. A different type of ring-contracted cadinane sesquiterpenoid is seen in the structure of mutisianthol (188). Another synthesis of oplopanone (189) has been reported (Scheme 31). ... 

Application of this methodology to the synthesis of ( + )-a-amorphene (zizazene, bicyclic sesquiterpene with a cadinane skeleton) shows that only the (.EJ-isomer 7 undergoes [3,3] sigmatropic shift. Obviously, steric interactions in the transition state of the corresponding (Z)-isomer suppress the rearrangement987. 

In his synthesis of the cadinane-sesquiterpene veticadinol (69), Lutz Tietze employed a sequence of Knoevenagel condensation of (i )-citronellal (66) and dimethylmalonate followed by an ene reaction provide 68 with the requisite trans stereochemistry in what was to become the decalin core of veticadinol 69. ... 

The rearrangement of 6/5-fused dienones has also been apphed to the synthesis of natural products. The 6P-isopropyl derivative of acetoxy ketone 45, obtained upon irradiation of the 6P-isopropyl derivative of dienone 44, was used in the synthesis of oplopanone. On the other hand, expansion of the A ring in the 5/6-fused methoxy ketone resulting from irradiation of the 6P-isopropyl derivative of le, allowed the synthesis of the cadinane sesquiterpene 3-oxo-a-cadinol and a-cadinoL ... 

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