Synthesis of 1H-2-naphtho[2,3-c]thiapyran-5,10-dione-2,2-dioxide, a 2-sulfone analogue of pentalongin

The synthesis of 1H-2-naphtho[2,3-c]thiapyran-5,10-dione-2,2-dioxide (2), a 2-sulfone derivative of the natural pyranonaphthoquinone pentalongin (1), was accomplished using the acid-catalysed cyclisation of the naphthoquinone sulfone acetal 6 as a key step in the synthesis.