A Focused Review of Synthetic Applications of Lawesson’s Reagent in Organic Synthesis

Lawesson’s reagent (LR) is a well-known classic example of a compound with unique construction and unusual chemical behavior, with a wide range of applications in synthetic organic chemistry. Its main functions were rounded for the thionation of various carbonyl groups in the early days, with exemplary results. However, the role of Lawesson’s reagent in synthesis has changed drastically, and now its use can help the chemistry community to understand innovative ideas. These include constructing biologically valuable heterocycles, coupling reactions, and the thionation of natural compounds. The ease of availability and the convenient usage of LR as a thionating agent made us compile a review on the new diverse applications on some common functional groups, such as ketones, esters, amides, alcohols, and carboxylic acids, with biological applications. Since the applications of LR are now diverse, we have also included some new classes of heterocycles such as thiazepines, phosphine sulfides, thiophenes, and organothiophosphorus compounds. Thionation of some biologically essential steroids and terpenoids has also been compiled. This review discusses the recent insights into and synthetic applications of this famous reagent from 2009 to January 2021.

Synthesis and Characterization of Benzylidene Derivatives of Benzothiazole

A series of some novel benzothiazole derivatives were synthesized from the 2-(4-aminophenyl) benzothiazol-5-ol, which was synthesized by the Jacobson method using Lawesson’s reagent. Benzylidene derivatives (P201-P205) were synthesized by catalyzed condensation and acylation method,named as 2-(4-((4 hydroxybenzylidene)amino) phenyl) benzothiazole-5-ol (P201), 2-(4-((4- methoxybenzylidene) amino)phenyl)benzothiazole-5ol(P202),2-(4-((4-chlorobenzylidene) amino)phenyl)benzothiazole-5-ol(P203), (4-((furan-2-ylmethylene) amino)phenyl)benzothiazole-5-ol(P204), Dimethyl(4(5hydroxy benzothiazol2yl)phenyl)carbonimidodithioate(P205)The structures of the compounds were confirmed by NMR and IR spectral data.

Thionation of Aminophthalimide Hindered Carbonyl Groups and Application to the Synthesis of 3,6′-Dithionated Pomalidomides

Herein, we present a new one-pot procedure for the 3,6′-dithionation of pomalidomide derivatives in which the key 3-position sulfur atom is preferentially installed at the desired (but sterically congested) carbonyl of the aminophthalimide system and with regiochemistry distinct from Lawesson’s Reagent thionation methods. When heated in 1,4-dioxane with P4S10–pyridine complex, pomalidomides are smoothly and reproducibly converted into their 3,6′-dithionated analogues in roughly 30% isolated yield and at various scales. While detrimental to the desired 3,6′-type outcome when employing Lawesson’s Reagent, we hypothesize that the pomalidomide aniline group instead facilitates P4S10-type thionation at the otherwise hindered 3-position carbonyl, contributing to the selectivity observed. When paired with classical methods of thionation, this approach offers an interesting and appealing addition to the synthetic toolbox, permitting facile late-stage access to complementary thionated pomalidomides in direct single-flask procedures.

A chromatography-free and aqueous waste-free process for thioamide preparation with Lawesson’s reagent

After completing the thio-substitution with Lawesson’s reagent, ethanol was found to be effective in the decomposition of the inherent stoichiometric six-membered-ring byproduct from the Lawesson’s reagent to a highly polarized diethyl thiophosphonate. The treatment significantly simplified the following chromatography purification of the desired thioamide in a small scale preparation. As scaling up the preparation of two pincer-type thioamides, we have successfully developed a convenient process with ethylene glycol to replace ethanol during the workup, including a traditional phase separation, extraction, and recrystallization. The newly developed chromatography-free procedure did not generate P-containing aqueous waste, and only organic effluents were discharged. It is believed that the optimized procedure offers the great opportunity of applying the Lawesson’s reagent for various thio-substitution reactions on a large scale.

Lewis base-free thiophosphonium ion: a cationic sulfur atom transfer reagent

Phosphorus(V) sulfide and Lawesson’s reagent are commonly used thionating reagents which are considered to operate after dissociation into highly reactive dithiophosphorane fragments. We report the synthesis and properties of a...