Reactions of 2-lithiated indoles with elemental sulfur. Formation of pentathiepino[6,7-b]indoles and indoline-2-thiones

The reactions of 2-lithiated indole and 1-methylindole with elemental sulfur have been studied, leading e.g. to a rational approach to pentathiepino[6,7-b]indoles 5 and 10. Notable amounts of the previously known tetrathiocino[5,6-b:8,7-b′]diindole 11 could be observed as a side reaction in the preparation of 10. Treatment of the anions of indoline-2-thiones 6 or 7 with sulfur also gave the pentathiepins 5 or 10, respectively. In addition, a convenient and clean lithiation route to indoline-2-thione (6) has been developed.