Synthesis of (±)-3-Demethoxyerythratidinone, an Alkaloid of Erythrina lithosperma BLUME

Abstract

an alkaloid of Erythrina lithoaperma Blume was synthesized in a racemic form by five different routes.3-Demethoxyerythratidinone 1, an alkaloid isolated from Erythrina lithos~erma Blume in 1973 by Barton et al.,' is one of the simplest erythrynan alkaloid which belongs to an alkenoid type.Although the syntheses of the dienoid type aromatic erythrinan alkaloids, erysotrine and erythraline, have been a c h i e ~e d , ~, ~' ~ total sythesis of the alkenoid type alkaloid has not been appeared so far.Here we describe five different synthetic routes to the titled alkaloid.A. From Z .8 -0 i o ~0 -7 ~-h v d ~o ~~e r y t h T i n a n ~ The 2.8-dioxo-7a-hydroxyerythrinan ethyleneacetal 2 is conveniently available from homoveratrylamine by 7 step reactions in aver-all yield of 65%.6,7Methanesulfonylation of 2 and heating of the resulting mesylate 38, mp 118-120'C.in benzene with OBU at 160-C (sealed tube, 8h) afforded two demesylated products 4 Imp 133-13S°C, 65.87(1H, brs), 38%1 and 5 [mp 2 0 0 -2 0 ~~~.65.87, 5.63 leach lH, s ) , Amax.233 and 285 nm, 51%], the both of which gave the same enone 6 ( 6 6.11, 1H.t, J=2 Hz) on acid hydrolysis and compound 5 gave compound