Syntheses of substituted 1,4-naphthoquinones by Diels–Alder addition of methoxycyclohexadienes to substituted 1,4-benzoquinones

Abstract

Additions of 1-methoxycyclohexa-1,3-diene to 2-methoxy-3-methyl-1,4-benzoquinone and to chloro-1,4-benzoquinone give Diels–Alder adducts which are coverted in high yield into substituted juglone methyl ethers. Reactions between 1-methoxy-3-methylcyclohexa-1,3-diene and methoxy-1,4-benzoquinone follow a similar course. Addition of 1,3-dimethoxycyclohexa-1,3-diene to chloro- or methoxy-benzoquinone affords a dihydrodibenzofuran rather than a Diels–Alder adduct.