The use of 3-acetoxy-1-trimethylsilylbutadiene in the synthesis of anthracyclinone derivatives

Abstract
The Diels–Alder reaction of quinizarin quinone (14) with 3-acetoxy-1-trimethylsilylbutadiene (15) affords a tetracyclic adduct, (±)-3-acetoxy-1,4,4aα,12aα-tetrahydro-1β-trimethylsilylnaphthacene-5,6,11,12-tetraone (16) in excellent yield. The simultaneous introduction of the C-7 trimethylsilyl substituent in this process allowed later ready conversion into a C-7 acetoxy group by treatment with lead tetra-acetate. The tetracyclic compound (16) was converted in a convenient multistep process into 4-demethoxydaunomycinone (51) in 41% overall yield from (14). Compound (51) was further elaborated to 14-acetoxy-4-demethoxydaunomycinone (4) by standard reactions, again in good yield (70% overall).