The two new phthalideisoquinoline hemiacetals rac‐egenine (3) and rac‐corytensine (4) are prepared by stereoselective DIBAL reduction of rac‐bicuculline (1) and rac‐adlumidine (2), respectively. The identity of egenine (3) with decumbensine as well as of corytensine (4) with epi‐α‐decumbensine and humosine A is postulated. The configuration around the anomeric center in natural (+)‐egenine (3), (+)‐corytensine (4) and (−)‐narcotine hemiacetal (7) is deduced as (7′S), (7′R) and (7′R), respectively. Copyright © 1991 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim