Anthracyclines. X. The enantiospecific synthesis of (–)-(7R)-7-Acetyl-7-hydroxy- 4,4-dimethoxy-5,6,7,8-tetrahydronaphthalen-1(4H)-one; a type I chiral dienone for the synthesis of 7-Deoxydaunomycinone

Abstract

8-Benzyloxy-5-methoxy-3,4-dihydronaphthalene-2-carboxylic acid (34) has been prepared by a four-step sequence from 5-methoxy-8-hydroxy-3,4-dihydronaphthalen-1(2H)-one. Condensation of the unsaturated acid (34) with ethyl (S)-prolinate in the presence of dicyclohexylcarbodiimide afforded the amide (35) which was enantioselectively cyclized to the bromo lactone (37). Debromination with tributyltin hydride and subsequent reaction of the lactone with methyllithium afforded (-)-(2R)-2-acetyl-8-benzyloxy-5-methoxy-1,2,3,4-tetrahydronaphthalen-2-ol. Removal of the benzyl ether by catalytic hydrogenation and oxidation of the resulting phenol with thallium(III) nitrate afforded the title chiral dienone.