Biomimetic approach to Galbulimina type I alkaloids

On treatment with trifluoroacetic acid the tetraene precursor underwent Boc deprotection, condensation and an iminium ion accelerated intramolecular Diels–Alder cycloaddition resulting in an iminium species , which was further converted into himbacine , himbeline and himandravine , three out of four Galbulimina type I alkaloids thus providing strong evidence for the proposed biogenesis of this important family of alkaloids.