Construction of the Pentacyclic Core and Formal Total Synthesis of (rac)‐Renieramycin T

A formal total synthesis of the antitumor marine natural product (rac)‐renieramycin T, which possesses a characteristic ecteinascidin‐type A ring in the renieramycin–saframycin core skeleton, was elaborated. The key steps in the synthesis of (rac)‐renieramycin T are a modified Pictet–Spengler cyclization of dialkylated oxomalonate derivatives and decarboxylation via a monocarboxylic acid derivative followed by stereocontrolled protonation of the enol intermediate. A key intermediate in our previous synthesis of renieramycin T was used, and the formal synthesis was accomplished in 21 steps from a known piperazine‐2,5‐dione derivative.