Synthesis of specifically O-alkylated anthraquinones by cycloaddition

✍ Scribed by Donald W Cameron; Geoffrey I Feuitrill; Glenn B Gamble; John Stavrakis

• Book ID: 104219196
• Publisher: Elsevier Science
• Year: 1986
• Tongue: French
• Weight: 290 KB
• Volume: 27
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)85117-5

✦ Synopsis

Cycloadducts from naphthoquinonoid dienophiles and l-methoxy-1-trimethylsilyloxy butadienes undergo controlled aromatisation to form chiefly cr-hydroxy-or a-methoxy-anthraquinones; this has led to synthesis of several natural O-methyl polyoxyanthraquinones. -In recently characterising cycloadducts of certain 1-methoxy-l-trimethylsilyloxy butadienes with quinonoid dienophilesl we noted their potential, through the mixed acetal function at Ci, for alternative aromatisation to either crhydroxy (A) or o-methoxy (B) products (Scheme). Other workers have observed examples of both products from related cyloadducts. 2,3 This paper systematises these processes, so that either can be made to predominate, for a range of cycloadducts (la,b -4a,b), all involving dienes derived by 0-silylation of ester -2 enolates . It then applies the resulting selectivities to synthesising for the first time several partially 0-methylated polyoxy anthraquinones of natural origin.