Pyranopyran derivatives related to citromycetin, and their sulphurization to give derivatives of 1-oxa-6,6-dithia(6a-SIV)pentalene and 1,6,6a-trithia(6a-SIV)pentalene

Abstract

Acetic anhydride and perchloric acid convert 3-acetyl-4-hydroxy-6-methylcoumarin into the half perchlorate of 2,9-dimethylpyrano[3,2-c][1]benzopyran-4,5-dione (IIb). Di-O-methylcitromycinone (III) has been obtained similarly. On treatment with boron sulphide, 2-methylpyrano[3,2-C][1 ]benzopyran-4,5-dione (IIa) gives 8-methyl-5,10-dioxa-9,9a-dithia(9a-S^IV)pentaleno[2,1-a]naphthalen-6-one (VIII). With phosphorus pentasulphide this gives a trithiapentalene derivative (XII), converted by acidic hydrolysis into 8-methyl-5,9-dioxa-9a,10-dithia(9a-S^IV)pentaleno[2,1-a]naphthalen-6-one (XIV).

Silicon disulphide transforms the dione (IIb) into a mixture of compounds (VIII) and (XII), along with a compound believed to have structure (XXII) containing the rare 1,6-dioxa-6a-thia(S^IV)pentalene nucleus.

The reference dioxadithia- and oxatrithia-pentalenonaphthalenones (XVIII) and (XIX) were obtained by condensing 4-hydroxycoumarin with 3-methylthio-5-phenyl-1,2-dithiolium sulphate and sulphurizing the product. A similar condensation of the salt with 4-hydroxy-6-methylchromen-2-thione afforded 6-methyl-2-phenyl-9-oxa-1,10,10a-trithia(10a-S^IV)pentaleno[1,2-b]naphthalen-4-one (XXI), a thionester sulphur atom participating in heterapentalene formation in preference to a benzoyl oxygen atom.