A New Route to Naphthofuran-4,9-diones from Thio-substituted 1,4-Naphthoquinones
Reaction of 2-phenylthio- or 2-ethylthio-1,4-naphthoquinones (1) and (2) with lithium enolates or pyridinium ylides was found to give alkylated 1,4-naphthoquionones (3)-(6) in high yields.Alkylated 1,4-naphthoquinones (5) and (6) were then effectively cyclized to 2-substituted naphthofuran-4,9-diones (8) by action of bromine in acetic acid.
Regioselective Addition Reaction of Lithium Enolates to Thio-Substituted 1,4-Naphthoquinones. Convenient Synthesis of a Naphthofuran-4,9-dione Ring System
The regioselective addition of lithium enolates to thio-substituted 1,4-naphthoquinones gave alkylated 1,4-naphthoquinones via 1,4-addition products.A phenacyl 1,4-naphthoquinone was cyclized to a naphthofuran-4,9-dione ring system.