Synthesis of Tetrahydroisoquinoline Antitumor Natural Products: Construction of Tricyclic Lactams Through Pictet-Spengler-Type Cyclization of N-Methyl-3-arylmethylpiperazine-2,5-dione with Ethyl Diethoxyacetate

6-Hydroxymethyl-7,8,10-trimethoxy-2,6-dimethyl-3,6,11,11atetrahydro-2H-pyrazino[1,2-b]isoquinoline-1,4-dione (10) was prepared stereoselectively by Pictet-Spengler-type cyclization of the O,N-acetal of 3-arylmethylpiperazine-2,5-dione (8) in high yield.This procedure provides an efficient route for the total synthesis of renieramycin G and cribrostatin 4.