Calcium‐Based Lewis Acid Catalysts

Abstract

Recently, Lewis acidic calcium salts bearing weakly coordinating anions such as Ca(NTf₂)₂, Ca(OTf)₂, CaF₂ and Ca[OCH(CF₃)₂]₂ have been discovered as catalysts for the transformation of alcohols, olefins and carbonyl compounds. High stability towards air and moisture, selectivity and high reactivity under mild reaction conditions render these catalysts a sustainable and mild alternative to transition metals, rare-earth metals or strong Brønsted acids.

CaCl2, Bisoxazoline, and Malonate: A Protocol for an Asymmetric Michael Reaction

“…1,2,3,4,5,6 Their use in asymmetric reactions has been studied since the pioneering work of Shibasaki and Yamada in 1998. 7 Nowadays, environmentally friendly reactions are of increasing interest.…”

CaII‐Catalyzed Alkenylation of Alcohols with Vinylboronic Acids

“…[8,9] For these reasons, ag eneral and mild reactionb etween alcohols and vinylboronic acids that avoids the use of noble transition-metals would be even more elegant. In this regard, calcium(II) salts display ah igh affinity towards alcohols to generate carbocation intermediates, [10] so they could be relevantc atalysts for new CÀCb ond-forming reactions. They are air-and moisture-stable and also weakly toxic.…”

Calcium‐Catalyzed Formal [2+2+2] Cycloaddition

“…[4] In a previous publication, we have been able to demonstrate that a reactive intermediate C, synonymous to B, can be generated with our highly efficient calcium based catalyst system [5] and give access to highly substituted cyclopropanes also in the absence of the stabilizing gold substituent. [6] Therefore, in pursuit of our program aiming at the development of carbocation cascade reactions for the generation of molecular complexity with simple non-transition metal catalysts, we reasoned that, following the same reaction pathway as the parent gold catalyzed reaction, trapping the intermediate C with carbonyl compounds will provide access to highly substituted formal [2 + 2 + 2] cycloaddition products.…”

“…Variation of the electronic properties of the carbonyl compound 5 shows that yields for cyclizations with aldehydes 5 bearing electron donating groups (entries 1/2, 11/12) are generally higher than with aldehydes bearing electron-withdrawing substituents (entries [3][4][5]13). Aryl moieties such as a naphthyl-or a furanyl substituent are well tolerated.…”