Synthesis of Substituted Thiophenes by Palladium-Catalyzed Heterocyclodehydration of 1-Mercapto-3-yn-2-ols in Conventional and Nonconventional Solvents

Abstract

A variety of readily available 1-mercapto-3-yn-2-ols 5 were conveniently converted into the corresponding thiophenes 6 in good to high yields in MeOH as the solvent at 50-100 °C in the presence of catalytic amounts (1-2%) of PdI(2) in conjunction with KI (KI:PdI(2) molar ratio = 10). The catalyst could be made recyclable employing an ionic liquid, such as BmimBF(4), as the solvent under suitable conditions.

One‐Pot Synthesis of 2,3,5‐Trisubstituted Thiophenes through Three‐Component Assembly of Arylacetaldehydes, Elemental Sulfur, and 1,3‐Dicarbonyls

“…Recently, the transition‐metal‐catalyzed direct C−H arylation of thiophenes has found to be an efficient tool for the thiophene diversification ,. With respect to annulation reactions, non‐readily available starting materials such as functional mercaptans,thioamides,, dialkynes,– and 1,2,3‐thiadiazoles, were frequently employed to generate substituted thiophenes through intermolecular or intramolecular cyclization. Also, few examples of multicomponent reactions led to the construction of thiophene rings from readily available chemicals ,.…”

Recent Advances in the Synthesis of Thiophene Derivatives by Cyclization of Functionalized Alkynes

“…A 5- endo - dig S -cyclization was also involved in the synthesis of substituted thiophenes 24 by Pd-catalyzed heterocyclodehydration of readily available 1-mercapto-3-yn-2-ols 23 , recently reported by our research group [64]. The cyclization reaction is catalyzed by PdI 2 in conjunction with an excess (10:1 molar ratio) of KI, and takes place either in MeOH at 50–100 °C (Table 2) or in an ionic liquid, such as BmimBF 4 , at 80 °C.…”

“…These are optimized conditions, after a careful study on the influence of the reaction parameters (such as the KI:PdI 2 molar ratio, the catalyst loading, and so on) on substrate reactivity and product yield. In the case of the reactions carried out in BmimBF 4 , the catalyst-solvent system could be recycled several times without appreciable loss of activity (Table 3) [64]. This protocol generalized the previous finding by Aponick and coworkers, who reported the Au/Ag-catalyzed transformation of 1-mercapto-4-phenylbut-3-yn-2-ol into 2-phenylthiophene, carried out using 5 mol % of Au[P( t -Bu) 2 ( o -biphenyl)]Cl and 5 mol % of AgOTf in THF at 40 °C in the presence of molecular sieves 4A [65].…”

Dichalcogenides/Oxone®‐Mediated Cyclization of (Z)‐Chalcogenoenynes under Ultrasound Irradiation

“…[52][53][54][55][56][57] The development of new methodologies for the synthesis of substituted telluro-, seleno-and thiophenes has been explored in the literature. Generally, these compounds are prepared by the cyclization of alkynes, dienes and diynes in the presence of inorganic chalcogen species [58][59][60][61] or via the intramolecular cyclization of organochalcogen compounds [62][63][64][65][66][67][68][69] and rearrangement reactions. [70] Among these procedures, Zeni and coworkers [71] described the cyclization of (Z)-chalcogenoenynes mediated by copper(II) salts (2.0 equiv) to afford 3-halochalcogenophenes (Scheme 1b).…”