Perhydro-9b-azaphenalene

PENTYLBENZOYL CHLORIDE, 61, 8 Perhydro-9b-azaphenalene, 61, 103 PERHYDRO-9b-BORAPHENALENE, 61,... 

In previous Reports the perhydro-9b-azaphenalene alkaloids derived from species of Coccinellidae (ladybird beetles) were discussed in the quinolizidine chapters while those isolated from the Australian shrub Poranthera corymbosa were included in the section devoted to miscellaneous alkaloids. In this Report the two groups of closely related alkaloids are considered together. 

The two stereoisomers of perhydro-9b-azaphenalene have been synthesized from the readily available perhydroboraphenalene (61) (Scheme 6). Oxidation yielded the triketone (62) which was converted by reductive amination into stereoisomer (63). This compound was transformed in six stages into isomer (64). 

Three 2a-methyl-perhydro-9b-azaphenalenes that constitute defensive substances of ladybird beetles were synthesized recently (cf. Vol. 7, p. 79), and an alternative synthesis has now been described (Scheme 2). The perhydrobora-phenalene (32) that was employed earlier to prepare unsubstituted perhydro-azaphenalenes (cf. Vol. 6, p. 101) was converted into the enamine quaternary ammonium salt (33) and thence into the allylamine (34). The allylamine epoxide was used to prepare ketone (36), which provided an efficient route to precoc-cinellin (35) by means of a Wittig reaction the same ketone was involved in the earlier synthesis of the alkaloid. 

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