Synthesis of anthracyclines via a claisen-diels-alder sequence

Naphthalene 16, a key intermediate for the synthesis of nogalamycin, was prepared in a six step sequence in 25% overall yield. The key step was a tandem Claisen-Diels-Alder sequence wherein the B- and C-rings were introduced in a single step. The naphthalene subunit was introduced by selenenylation of a β-diketone.