Abstract
Methylenedioxy- and dimethoxy-derivatives of the hexahydrocyclopenta[e]phenanthridine ring system. (21a) and (21b), have been synthesised stereospecifically in six steps starting from piperonal (50% overall yield) and dimethoxybenzaldehyde (27% overall yield), respectively. Piperonal was converted into nitrostyrene derivative (13a) by the known procedure; compound (13a) on reaction with butadiene sulphone afforded the butadiene cycloaddition product (14a) which reacted with methyl acrylate in base to yield nitro-ester (15a) in a stereospecific Michael addition. Reductive cyclisation of compound (15a) using zinc and hydrochloric acid gave spirolactam (16a) which was reduced with lithium aluminium hydride to yield spiropyrrolidine (18a); this compound was converted into the pentacyclic system (21a) by reaction with formaldehyde under Pictet-Spengler conditions. Thiolactam (17a), was obtained from reaction of lactam (16a) and phosphorus pentasulphide, and was methylated with methyl iodide to give lactlminium salt (19a) which reacted with sodium borohydride to yield thiolactim derivative (20a). The route to tetracyclic compound (21b) directly paralleled this sequence.
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