Microwave-assisted efficient thiolate-catalysed homo- and crossed intermolecular Tishchenko reactions

Abstract

Recently, the first efficient intermolecular crossed Tishchenko reactions were reported. The utility of these processes is curtailed by long reaction times of up to 4 days (at reflux). Herein we report that these reactions are highly susceptible to acceleration by microwave irradiation-allowing fast, efficient, high-yielding coupling to proceed in 10-180 min.Fig. 1 The thiolate catalysed homo-Tishchenko reaction.

Catalytic bond forming reactions promoted by amidinate, guanidinate and phosphaguanidinate compounds of magnesium

“…Subsequent work with main group elements includes compounds of Li, 73,74 Na, 73,75,76 K, 73 and most recently Zn. 77 Magnesium reagents have been used in the presence of thiolate 18,19,78 and selenide anions 79 to promote this coupling reaction. We have previously communicated our work in this area with amidinate compounds 11 and 13, 22 and guanidinates 16 and 17.…”

Selenide Ions as Catalysts for Homo- and Crossed-Tishchenko Reactions of Expanded Scope

“…However, it has been regarded more as a mechanistic curiosity than as a powerful synthetic tool by contemporary chemists, despite over a century of research, largely due to a narrow substrate scope, which until recently was limited (in an intermolecular context) to the homocoupling of aldehydes, in often variable yields . Inspired by the mode of action of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase, involving hydride transfer from a hemithioacetal-based intermediate ( A , Scheme ), we recently developed the first thiolate-catalyzed Tishchenko processes ( A , Scheme ). , The smooth conversion of benzaldehyde ( 1 ) to the corresponding benzoate ester 2 upon exposure to an in situ formed simple bromomagnesium thiolate derived from 4- tert -butylbenzylmercaptan ( 3 ) was possible in excellent yield. The proposed mechanism ( B , Scheme ) involves initial attack of the thiolate on the aldehyde to furnish 4 , which then transfers a hydride to another molecule of 1 to form both the alkoxide 5 and thioester 6 , which then couple to give 2 and the regenerated catalyst, which re-enters the cycle.…”

Synthesis, Structures, and Reactivities of Guanidinatozinc Complexes and Their Catalytic Behavior in the Tishchenko Reaction

“…A number of catalysts for the Tishchenko reaction have been reported, including metal, metalloid, and nonmetal compounds, such as Na, Mg, Al, Ca, Ba, Sr, B, Fe, Ru, Os, Hf, Zr, La, Y, and Sc . Recently, a magnesium guanidinate compound, Th­(IV) compounds, Ni(0)/NHC, including an organic compound thiolate, and selenide ions have been reported as effective catalysts in the Tishchenko reaction. But, to the best of our knowledge, there have been no reports on zinc compounds used as the catalyst of the Tishchenko reaction. …”

“…1 H NMR (C 5 D 5 N): δ (ppm) 0.97 (q, J = 7.9, 4 H, ZnCH 2 CH 3 ), 1.09 (t, J = 6.9, 6 H, ZnCH 2 CH 3 ), 1. 15 Method 2. A stirred suspension of compound 10 (0.62 g, 1.0 mmol) in hexane (40 mL) and diethylzinc (1.0 mL of a 1.0 M solution in hexane, 1.0 mmol) was stirred at room temperature for 8 h to afford a cloudy mixture, which was filtered.…”