Abstract
Coleon B (1a), described by Eugster1 in 1969, proved to be an exceptional member of the coleons with the extended conjugation reaching into the C.19 nor ring A. Using simple models, available from methyl O-methyl podocarpate (2a) we explored methods to introduce the proper C.2 to C.7 functionalities. The known2 hydro-demethoxycarbonylation of the α,β-unsaturated ketone 3a in the presence of 3-quinuclidinol which affords the enone 4 gave us a model for placing a C.3 — C.4 double bond which was realized by treatment of 4 with N-bromosuccinimide. The presumed C.4 bromo intermediate spontaneously eliminated hydrogen bromide to extend the conjugation to give 5a (H nmr : 1.38 (s, CH3C.10), 1.98 (fine m, CH3C.4), 3.90 (s, CH3O), 6.07 (m, H-3), 6.39 (s, H-C.6) δ). The Ratcliffe-Rodehorst reagent oxidised the allylic methylene group to give a useful yield of the diene-dione 6a (H nmr : 1.53 (s, CH3C.10), 2.27 (d, J=1.2 Hz, CH3C.4), AB q. centred at 2.92 (J=16 Hz, H2C.1), 3.93 (s, CH3O), 6.24 (br. s, H-C.3), 6.73 (s, H-C.6) δ) which has similar but not identical functionality to coleon B.