Ring-cleavage of phthalidisoquinoline alkaloids by ethyl chloroformate

Article abstract of DOI:10.1002/ardp.19923250710

Degradation of (-)-α-narcotine (5), (-)-β-narcotine (6), and (-)-β-hydrastine (7) with ethyl chloroformate (ECF) affords the chloro-urethans 9 and 18, respectively. Diastereomer 9-I is easily hydrolyzed to the hydroxy-urethan 10, whilst 18 is converted to the methoxy-analogue 19. The stilbene lactone 11 is obtained from 9-I by treatment with DBU, the analogous stilbene 17 arises already when 7 is reacted with ECF. - Hydroxy-urethan 10 - a phenylogous aldol - is split by OH^- to aldehyde 13 and to meconine (14). LiAlH₄-reduction of 10 yields the stereochemically homogenous triol 15, which is cyclized to diastereomers of the 3-phenyl-isochroman 16 under acidic conditions.