The Eschenmoser sulfide contraction method and its application in the synthesis of natural products

Eschenmoser‐Coupling Reaction Furnishes Diazenyl‐1,2,4‐triazole‐5(4H)‐thione Derivatives

“…Herein we reported the results of our investigation on the reactions of N ‐substituted 2‐phenylhydrazinecarbothioamides 1 a‐e and 2,3,5,6‐tetrachloro‐1,4‐benzoquinone ( p ‐CHL, 2 ) using the Eschenmoser‐contraction method, (Scheme ) to yield 1,2,4‐triazol‐5(4H)‐thione which might have biological activity as demonstrated by related derivatives..…”

New syntheses of (±)-tashiromine and (±)-epitashiromine via enaminone intermediates

“…One of the most versatile methods for preparing the enaminones of interest is the Eschenmoser sulfide contraction of thiolactams with α-halocarbonyl compounds [24–25], which was originally described by Eschenmoser and co-workers in 1970–1971 [26–27]. We were interested to examine the impact of different electron-withdrawing substituents at what would become the 8-position of the indolizidine skeleton.…”

Base‐Mediated Cyclization of 3‐[2‐(2‐Oxo‐2‐phenylethyl)‐1‐pyrrolidinyl]propanenitrile to 7‐Phenyl‐1,2,3,7,8,8a‐hexahydroindolizine‐6‐carbonitrile: What Lies Between?

“…The enaminone 6 was prepared essentially as described previously [12] by Eschenmoser sulfide contraction [14,15] between phenacyl bromide and the thiolactam 11 (Scheme 1, upper line). The reaction could be performed on a six-gram scale, and 6 was obtained in 86 % yield without the need for chromatographic purification.…”