Reactions of quinones with aromatic ethers. Part III. Arylbenzoquinones and dibenzofurans from 2,5- and 2,6-dichlorobenzoquinone and veratrole

Heteroatom-Embedding Annulative π-Extension (Hetero-APEX) Reactions: An Overview

“…Figure 6 Acid-mediated oxa-APEX reaction of veratrole using 2,5-dichloro-1,4benzoquinone. 15 In 2005, Musgrave and coworkers reported an oxa-APEX reaction affording polycyclic furan 9 from veratrole (1) or anisole (7) and 9,10-phenanthrenequinone (8) (Figure 7). 16 In the presence of a catalytic amount of SnCl4•5H2O at 180 °C without solvent, electron-rich arenes 1 and 7 are were considered to attack one of the carbonyls in the electron-deficient 1,2-diketone to afford a Friedel-Crafts type reaction intermediate A.…”

“…In 1974, the first example of an oxa-APEX reaction (also the first example of a hetero-APEX), was reported by Musgrave and co-workers. 15 They discovered that the reaction using an excess amount of 2,5-dichloro-1,4-benzoquinone (2) constructs a benzofuran ring onto 1,2-dimethoxybenzene (veratrole, 1) under acidic conditions, giving a mixture of dibenzofuran derivative 3 (38%), diarylbenzoquinone 4 (38%), and 2,3, 6,7,10,11-hexamethoxytriphenylene (17%) in one step (Scheme 5a). 15 Through control experiments using an excess amount of 1, this oxa-APEX reaction seems to proceed through a conjugate addition of 1 to quinone 2 via intermediate A, giving monoarylated benzoquinone 6 (Scheme 5b).…”