NOVEL ROUTE TO 4,5,6,7-TETRAHYDROINDOLES AND PYRROLES

Treatment of cyclic unsaturated amides, 1,4,5,6,7,7a-hexahydro-2H-indol-2-ones 1, with Lawesson's reagent [2,4-bis-(p-methoxyphenyl)-1,3-dithia-2,4-diphosphetane 2,4-disulfide] yielded unexpected products, 4,5,6,7-tetrahydroindoles 2, in moderate yield. Reduction of compounds 1 with diisobutylaluminium hydride also gave compounds 2 in good yield. In contrast, treatment of monocyclic 1,5-dihydropyrrol-2-ones 5 with Lawesson's reagent gave the thionation products, 1,5-dihydropyrrole-2-thiones 7, as main products, along with pyrroles 6.