Starting from homopiperonylamine or phenethylamine with homophthalic
anhydride or 3,4-methylenedioxyhomophthalic acid, respectively,
facile syntheses of the reported structures of (±)-gusanlung
D and (±)-isogusanlung D were accomplished via regioselective reductive
dehydration of the corresponding homophthalimides followed by an
intramolecular acid-catalyzed or radical cyclization pathway. Starting
from the corresponding suitably ortho-halogenated
homophthalimides, the syntheses of dehydrogusanlung and dehydroisogusanlung
D were completed via regioselective reductive dehydration followed
by an intramolecular Heck coupling reaction as the key steps. The
analytical and spectral data obtained for all four synthetic compounds
differed from the reported data for natural gusanlung D, and therefore
the structural assignment of the natural product needs to be revised.
homophthalic anhydride, homopiperonyl amine - reductive
dehydration - Heck reaction - gusanlung D
