N-2-Glycosyl Thiosemicarbazides from N-3-Glycosyl Oxadiazolinethiones Obtained from 2-S-Glycosyl Oxadiazolines via Mild Thermal S→N Migration of the Glycosyl Moiety

Abstract

A new class of N-2-glycosyl thiosemicarbazides has been synthesized from N-3-glycosyl oxadiazoline-thiones. Glycosylation of 5-(1H-indol-2-yl)-1,3,4-oxadiazolin-2(3H)-thione with acetylated α-glycosyl halides by grinding in the presence of basic alumina gave the S-glycosyl oxadiazoles while in the presence of Hg(II) chloride N-3 glycosyl analogues were obtained. In the presence of Et₃N or K₂CO₃, mixtures of S- and N-glycosylated isomers were obtained as products. The S→N glycosyl migration under catalyst-free mild thermal conditions was described, and a new class of N-2-glycosyl thiosemicarbazides was synthesized from N-3-glycosyl oxadiazolinethiones by ring cleavage of the oxadiazolole ring by treatment with ammonia in methanol.

Key words

indolyloxadiazolines - S-glycosides - N-glycosides - glycosylation - thiosemicarbazides - thermal rearrangement

References and Notes

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19

Experimental Procedure
The S-glycoside 5 (0.5 mmol) was fused under atmospheric conditions, and the thermal conversion was monitored by TLC. After completion of the reaction (5-10 min), the fused mass was crystallized from EtOH to afford the corresponding N-glycosides 8. A mixture of 8 (5.0 mmol) in MeOH (10 mL) and NH₃ solution (32%, 5 mL) was stirred at 0 ˚C for 1 h, then allowed to reach ambient temperature. After 6 h, the solvent was evaporated in vacuo, and the residue was purified by column chromatography (EtOAc-MeOH-CHCl₃ = 4:3:3) to give 11; mp 212-214 ˚C.