Treatment of phthalideisoquinolines such as α- (1) and β-narcotine (2) as well as β- (3) and α-hydrastine (4) with ethyl chloroformate (ECF) at room temperature afforded, via the chloro-carbamates, the corresponding diastereomeric carbinols with high stereoselectivity. Instrumental analyses of each diastereomeric pair indicate that the major isomers derived from α- and β-narcotine as well as from α- and β-hydrastine are enantiomers of each other. The absolute configuration of the major carbinol 6a from α-narcotine (1) was determined by X-ray analysis. The probable difference between the reaction course of α-and β-narcotine is discussed. On the other hand, treatment of α-narcotine with ECF under reflux furnished Z-(8) and E-(9) enol lactones, while only the Z-isomer 12 could be isolated from the degradation of β-hydrastine (3) even at room temperature.
Ring-cleavage of Phthalidisoquinoline Alkaloids by Ethyl Chloroformate
作者:Silvia von Angerer、Erwin von Angerer、Reinhard Ambros、Wolfgang Wiegrebe
DOI:10.1002/ardp.19923250710
日期:——
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