Electrochemical oxidative synthesis of 1,3,4-thiadiazoles from isothiocyanates and hydrazones

Abstract

A 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-catalysed electrochemical synthesis of 2-amino-1,3,4-thiadiazoles from isothiocyanates and hydrazones is presented. This protocol is mild, practical, metal-free and exogenous oxidant-free, and features a broad substrate scope. Extensive mechanistic...

Electro-organic synthesis: an environmentally benign alternative for heterocycle synthesis

“…Ma et al 126 developed a metal and oxidant-free synthesis of 1,3,4-thiadiazoles using the electrochemical oxidative method. The pre-screening of the reaction conditions was performed with isothiocyanatobenzene ( 146a ) and benzylidene hydrazine ( 148a ) using DDQ as catalyst.…”

“…Claraz et al 120 reported the electrochemically catalysed multicomponent synthesis of CF 3 -substituted imidazolines and oxazolidines via trifluoromethylation of allylamine/[3+2] cycloaddition. The reaction conditions were optimised using N-tosyl allylamine (126) and acetonitrile (127a) as model substrates and Langlois reagent (87) as trifluoro-methylating agent. The reaction was performed in an undivided cell furnished with nickel as a cathode and carbon as anode.…”

“…In the proposed mechanism, initially the formation of the CF 3 radical from 87 via the SET mechanism with the formation of SO 2 gas was proposed. Then, radical 87B was added to the double bond of substrate (126) and yielded benzylic radical 128A, which further oxidised to cationic intermediate 128B. The intermediate 128B thus formed reacted intramolecularly via its N-atom to yield aziridine (128C).…”

Recent Advances in Electrochemical Cascade Cyclization Reactions

“…Review / Short Review [71][72][73][74] The electrochemical sulfonylation/cyclization reactions between 2-alkynylthioanisoles 131 and sodium sulfinates 132 using nBu4NBF4 or nBu4NBr as electrolyte delivered sulfonated benzothiophenes 133 in 43-87% or up to 86% yields. 71,72 Thiazoles 136 and dihydrothiazoles 138 can be synthesized in 31-96% yields and up to 93% yields respectively from the electrochemical reactions of thiourea 135 with enamines 134 or enaminones 137 in the presence of HCl (aq) or trifluoromethanesulfonic acid (TfOH) in MeOH or R 4 OH.…”

“…73 Under the catalysis of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), the electrochemical reactions of isothiocyanates 139 and hydrazones 140 afforded 40-84% yields of 2-amino-1,3,4thiadiazoles. 74 Scheme 25 Electrochemical cascade cyclization for the synthesis of sulfonated benzothiophenes, thiazoles, dihydrothiazoles and 1,3,4thiadiazoles.…”