Chiral Ferrocenyl−Iodotriazoles and −Iodotriazoliums as Halogen Bond Donors. Synthesis, Solid State Analysis and Catalytic Properties.

Abstract

Despite the increasing number of applications based on halogen bond (XB), asymmetric catalysis purely based on such supramolecular interactions still remains a huge challenge. The first step toward its development is the design of appropriate XB chiral donor molecules with good catalytic properties. In this context, we report the synthesis of a series of iodinated compounds based on the triazole or triazolium ring and possessing the planar chirality of ferrocene. Their XB donor property was attested by X‐ray diffraction analysis, showing short I⋅⋅⋅N and I⋅⋅⋅F interactions in the triazole‐based derivatives and in the tetrafluoroborate salt of a idodotriazolium, respectively. The potential of these compounds to act as XB‐based catalysts was demonstrated in the aza‐Diels‐Alder reaction involving an imine and a diene. Whereas triazole‐based derivatives were inactive in this reaction, the triflate salts of iodotriazoliums delivered the expected cycloadduct with high yield.

Recognition in the Domain of Molecular Chirality: From Noncovalent Interactions to Separation of Enantiomers

“…Low asymmetric induction (6.4%) was observed in the reaction with an enantiopure bidendate catalyst. 824 Exploring the asymmetric pnictogen-bonding catalysis, Tan and coauthors reported an enantioselective transfer hydrogenation of benzoxazines catalyzed by a novel chiral antimony cation/ anion pair. 825 The catalyst showed remarkable efficiency and enantiocontrol even at 0.05 mol % loading.…”

“…Good catalytic activity was observed at room temperature with an iodotriazolium triflates in an aza-Diels–Alder reaction, and the best performance was achieved with a bidendate derivative. Low asymmetric induction (6.4%) was observed in the reaction with an enantiopure bidendate catalyst . Exploring the asymmetric pnictogen-bonding catalysis, Tan and co-authors reported an enantioselective transfer hydrogenation of benzoxazines catalyzed by a novel chiral antimony cation/anion pair .…”

Stereoselective Processes Based on σ-Hole Interactions

“…More recently, our groups described the bis-iodotriazolium catalyst 38 bearing planar chirality of ferrocene. This bidendate catalyst performed efficiently in the aza-Diels–Alder reaction between imine 39 and Danishefsky diene 40 , but product 41 was obtained with a very low ee of 6%, probably because of the high flexibility of the two iodotriazolium arms of the catalyst [ 99 ] ( Figure 20 ).…”

Unravelling functions of halogen substituents in the enantioseparation of halogenated planar chiral ferrocenes on polysaccharide-based chiral stationary phases: experimental and electrostatic potential analyses

“…Since, halogenated ferrocenes have appeared as key intermediates for accessing polysubstituted ferrocenes [12]. More recently, iodinated ferrocenes turned out to be involved in halogen bond (XB) in solid state [13,14], and even in solution with emerging application as organocatalyst in organic synthesis [13,15].…”