Synthesis of Sulfur Heterocycles from Dithiocarbamates

Significance

Reported is the synthesis of dibenzo[b,d]thiophenes 3, [1]benzothieno[2,3-b][1]-benzothiophenes 6 and the unknown [1]benzo-thieno[2,3-b][1]benzofurans 6 from readily available bi(het)aryls 1 and 4. Magnesiation of 1 and 4 followed by a trapping with tetramethylthiuram disulfide afforded dithiocarbamates 2 and 5 which undergo cyclization under basic conditions to get 3, 6, and 7 in good overall yields. [1]Benzo-thieno[2,3-b][1]benzothiophene 10 was prepared in a similar way from 3-Br-2-I-benzo[b]thiophene. Interestingly, those S-heterocycles were regio­selectively aluminated without assistance from ­heteroatom-directing groups using aluminum amide 8. Transmetalation followed by electrophilic quench afforded further functionalized products 9, 11, and 12.