A new synthesis of thiophenes and thiapyrans

Summary

4:5-Benzothionaphthene (II) was obtained by theα-cyclization ofβ-naphthylω-dimethoxyethyl sulphide (I), and the hitherto unknown naphtho-(1′:8′-bc)-thiapyran (IV) by theperi-cyclization ofα-naphthylω-dimethoxyethyl sulphide (III).

Naphthalene-1:5-dithiol was obtained in 85% yield by an improved method. Condensation of naphthalene-1:5 and 2:6-dithiols with two molecules of bromoacetaldehyde dimethyl acetal gave (VIII) and (XI). The former cyclized in theperi-positions to give “1:6-thiapyrene” (IX) which was orange in colour, and the latter cyclized in theα-positions to give 4:5, 5′:4′-dithionaphthene (XII), an isoster of chrysene which was colourless. Chrysene and (XII) gave similar absorption spectra, which were markedly different from the absorption spectrum of (IX).