Abstract1,3‐Disubstituted tetrahydro‐oxazolo‐isoquinolinones 19a,b were obtained from phenylalanine in seven steps and 42% overall yield by Katritzky’s benzotriazole method. The tricyclic oxazolidinone 19a was further converted into amino alcohol 10 by employing a chemoselective reduction of the ester group with LiBH4/MeOH. Compound 10 and the corresponding 1‐unsubstituted tetrahydroisoquinoline alcohol 11 were converted into aldehydes 27 and 33, which cyclized in the presence of different Lewis acids to give the substituted azepino[1,2‐b]isoquinolines 34 and 35, respectively, which are key structural features of the alkaloid quinocarcin. The stereoselectivities of the Lewis‐acid‐catalyzed hetero‐ene reaction are highly dependent on the substitution pattern and the type of Lewis acid. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)