Phenoxathiine 10,10-dioxides

Smiles rearrangement was observed also in base-catalyzed cyclization of 2-hydroxy-2 -nitrodiphenylsulfones leading to low yields (about 5%) of phenoxathiine 10,10-dioxides (34JCS422, 56JA5357). However, this type of compounds can be easily prepared by other methods (05CB1411, 06CB1340). 

SCHEME 73 Thia-Fries rearrangement involving arynes to form phenoxathiin-dioxide [100]. 

Oxanthrene is cleaved by lithium in THF at 25 °C and the product obtained by quenching the intermediate with carbon dioxide is the carboxylic acid (60) in 56% yield. On heating with lithium in THF for 7 h the main isolated product is catechol. Cleavage of phenoxathiin with lithium in ether occurs at C-5 to give, after carboxylation, product (61), analogous to those obtained from oxanthrene, and the disulfide of this same compound. However, this reaction, when run in THF at 50°C and terminated by carboxylation, produced 2-thiolphenol and phenoxathiin-4,6-dicarboxylic acid, the product of dimetallation <58JA380>. 

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