Synthesis of New Functionalized 2-Alkylsulfanyl-5-(1H-indol-2-yl)-1,3,4- Oxadiazole and a Facile Thio-Aza-Claisen Rearrangement of the S-Allyl Analog

The S-alkylated indolyloxadiazoles 2a-l were obtained regioselectively by alkylation of 5-(1H-indol-2-yl)- 1,3,4-oxadiazole-2(3H)-thione 1, using TEA as acid scavenger. Alkylation of 1 with 1-bromopropane, 1-bromobutane, 1- bromoundecan, in the presence of K2CO3, yielded the N-alkylated products 3i-j,m in addition to the S-alkylated analogs 2i-j,m. A facile thio-aza-Claisen rearrangement (S??N allylic rearrangement) of the S-allyl-oxadiazole 2k to the N-allyl analog 3k was achieved in excellent yield. Further allylation of 2k and 3k in the presence of K2CO3 led to allylation of the NH indole ring producing 5 and 6, respectively. Benzylation of 1 in the presence of K2CO3 yielded 7 which resisted the S→N migration of the benzyl group. The 1H NMR, 13C NMR and mass spectra confirmed the structures and differentiated between the N- and S-alkylated products.