Reactivity studies of [1]benzothieno[3,2-b][1]benzofuran

Electrophilic substitution and metallation reactions of the title compound 1 were studied. Bromination, acetylation, benzoylation, formylation, and ni tration usually afforded nonseparable mixtures of 2- and 7-substituted deri vatives as the main product. Disubstitution reactions preferably led to 2,7 -disubstituted derivatives. [1]Benzothieno[3,2-b][1]benzofuran 10,10-dioxid e (17) and [1]benzothieno[3,2-b][1]benzofuran 10-oxide (18) can be selectiv ely obtained by oxidation of 1. Mononitration of 17 and 18 led selectively to corresponding 7-nitro derivatives 19 and 21, respectively. Only sulfoxid es 19 and 20 were successfully reduced. Reduction of the 5-oxide moieties w as successful only at the sulfoxide stage. Metallation of 1 with butyllithi um preferably proceeds in positions 1 and 6; subsequent reaction with methy l iodide or carbon dioxide led to the corresponding dimethyl derivative 25 or esters 26 and 27, respectively. An unusual addition of butyllithium to t he central double bond of 1 was also observed in a small extent producing 9 b-butyl-4b,9b-dihydro[1]benzothieno[3, 2-b][1]benzofuran-4b-ol (29). The st ructures of all products were elucidated by NMR.