Sustainable Access to 5‐Amino‐Oxazoles and Thiazoles via Calcium‐Catalyzed Elimination‐Cyclization with Isocyanides

Abstract

Herein, we report a sustainable, modular, rapid and high‐yielding transformation to afford densely functionalized 5‐aminooxazoles and thiazoles. The reaction is tolerant to a wide range of functional groups and is typically complete in under 30 min. Furthermore, the described transformation is inherently green in relation to the catalyst and solvent choice as well as producing environmentally benign alcoholic by‐products.

Calcium Bistriflimide-Mediated Sulfur(VI)–Fluoride Exchange (SuFEx): Mechanistic Insights toward Instigating Catalysis

“…Second, like group 3 compounds, Ca 2+ is a strong Lewis acid, especially when coordinated to weakly binding ligands such as fluorides (F – ), triflates (OTf – ), bistriflimides (NTf 2 – ), or 1:1 bistriflimide/hexafluorophosphate (PF 6 – ) counterions. These Ca 2+ salts form Lewis acid/base adducts to activate otherwise weakly electrophilic compounds such as alcohols, − carbonyls, − olefins, − and boronic acids for subsequent coupling with nucleophilic reagents, notably also with relatively high tolerance to air and moisture. In our recent reports, we employed Ca 2+ salts for the first time to activate a different class of compoundssulfur­(VI) fluorides. , …”

Aza-[4 + 2] cycloadditions employing catalytically derivedN-acyliminium ions

“…Our work began by taking advantage of our previously reported methodology to access N-acyliminium ions via catalytic dehydration. [11][12][13][14] We therefore began our investigation using these conditions, employing hydroxyisoindolinone 1 and dimethylbutadiene (2a) as model substrates (Table 1). As shown, optimisation of temperature, solvent, and catalyst loading led to conditions that afforded the [4 + 2] product in high isolated yield.…”