A new route to naphtho[2,3-b]furan-4,9-diones from thio-substituted 1,4-naphthoquinones
Abstract
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-naphthoquinones (3)–(6) in high yields. Alkylated 1,4-naphthoquinones (5) and (6) were then effectively cyclized to 2-substituted naphtho[2,3-b]furan-4,9-diones (8) by action of bromine in acetic acid.