Degradation of some Phthalideisoquinolines with Ethyl Chloroformate-Stereochemical Aspects

Abstract

Treatment of phthalideisoquinolines such as α- (1) and β-narcotine (2) as well as ß-(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.