A new synthetic access to 2-N-(glycosyl)thiosemicarbazides from 3-N-(glycosyl)oxadiazolinethiones and the regioselectivity of the glycosylation of their oxadiazolinethione precursors

Expeditious Green Synthesis of Novel 4-Methyl-1,2,5,6-tetraazafluoranthen-3(2H)-one Analogue from Ninhydrin: N/S-Alkylation and Aza-Michael Addition

A straightforward green synthesis of 4-methyl-1,2,5,6-tetraazafluoranthen-3(2H)-one 6 is reported from ninhydrin 1 via condensation with ethyl acetoacetate, followed by cyclization with hydrazine hydrate in water as a benign solvent. Tetraazafluoranthen-3-thione 7 was obtained using Lawesson's reagent. N-alkylated tetraazafluoranthen-3-one 8-12 and S-alkylated analogues 13-15 were synthesized via alkylation. The investigation of the unique reactivity of 4-methyl-1,2,5,6-tetraazafluoranthen-3(2H)-one/thione toward the alkylation and aza-Michael additions was explored.

Synthesis of New Functionalized Indoles Based on Ethyl Indol-2-carboxylate

Successful alkylations of the nitrogen of ethyl indol-2-carboxylate were carried out using aq. KOH in acetone. The respective N-alkylated acids could be obtained without separating the N-alkylated esters by increasing the amount of KOH and water. The use of NaOMe in methanol led to transesterification instead of the alkylation, while the use of NaOEt led to low yields of the N-alkylated acids. Hydrazinolysis of the ester gave indol-2-carbohydrazide which then was allowed to react with different aromatic aldehydes and ketones in ethanol catalyzed by acetic acid. Indol-2-thiosemicarbazide was used in a heterocyclization reaction to form thiazoles. The new structures were confirmed using NMR, mass spectrometry and X-ray single crystal analysis.

Inverse neighboring group participation: explanation of an unusual S→N alkyl migration of isothiuronium salts containing a lactone group

A detailed experimental and DFT study of the S to N alkyl migration of substituted S-(1(3H)-isobenzofuranon-3-yl)isothiuronium bromide to N,N'-dimethyl-N-(3-oxo-1,3-dihydro-2-benzofuran-1-yl)thiourea provided evidence for the existence of an unusual double displacement mechanism involving two consecutive back-side S(N)2 reactions where a carboxylate anion has a crucial role both as a leaving group as well as an internal nucleophile. The thiazetidine zwitterionic species that is involved in this mechanism as an intermediate was characterized by infrared multiphoton dissociation spectroscopy and was trapped with methyl iodide. It was found that the intermediate has a structure of a free ion pair. The double-displacement mechanism can be considered as a new type of inverse lactone neighboring group participation.