Strong Affinity of Triazolium-Appended Dipyrromethenes (TADs) for BF4−

Because BF4− is a labile, non- or weakly coordinating anion, it is generally chosen by chemists who do not want the anion to interfere with the associated cation. Herein, we demonstrate that BF4− actually strongly binds to triazole-appended dipyrromethenes (TADs). In particular, HETCOR NMR experiments and DFT calculations were used to rationalize the results observed with anion titrations. Hence, special care should be taken when considering that BF4− is innocent.

C–H Functionalization Reactions of Phenyl and Vinyl Carbocations Paired with Weakly Coordinating Anions

Carbocations have played a central role in the chemical sciences for over a century. In a synthetic setting, most methods utilize stabilized tricoordinate carbocations, while there are far fewer examples of reactions featuring nonstabilized dicoordinate cations. Here, we provide an overview of recent developments in the generation of high-energy carbocations mediated by weakly coordinating anions and the C–H insertion reactions of such carbocations. Moreover, we discuss mechanistic studies of these catalytic C–H insertion reactions aimed at furthering our understanding of the reactive nature of these rarely invoked cationic intermediates.1 Introduction2 Background: Phenyl Carbocations3 Silylium/Carborane-Catalyzed C–H Insertion Reactions of Phenyl Carbocations4 Silane-Fueled, Weakly Coordinating Anion-Catalyzed, Reductive C–H Insertion Reactions of Vinyl Carbocations5 C–H Insertion Reactivity of Vinyl Carbocations under Basic Conditions6 Conclusion and Outlook

Terpene Tail-to-Head Polycyclization Mediated by Small Molecule Catalysts: A Weakly-Coordinating Anion Approach

<p>Biomimetic total synthesis has played a pivotal role in the development of synthetic organic chemistry. In particular, efforts aimed at mimicking the head-to-tail (HT) cation–π cyclization cascades invoked in terpene biosynthesis, such as those catalyzed by type-II cyclases, have led to a multitude of new synthetic methods, chemical concepts, and total syntheses over the past century. Conversely, synthetic methodology that mimics tail-to-head (TH) cation–π cyclization cascades, mediated by Mg²⁺ type-I terpene cyclases, remains elusive in organic synthesis, despite key roles in the biosynthesis of privileged therapeutic molecules such as taxol and artemesinin. Here we report that Li⁺/weakly-coordinating anion (WCA) salts catalyze the TH polycyclization of linaloyl fluoride, leading to high-yielding mixtures of polycyclic terpene natural products including cedrenes, cadinadiene, epizonarene, and 𝛿-selinene. The examples reported herein are the first small molecule-catalyzed TH polycyclization reactions enabling the shortest (formal) total synthesis of (<i>±</i>)-artemisinin. Moreover we apply this strategy to the diterpene geranyllinaloyl fluoride, resulting in a two-step total synthesis of the tricyclic core of the gersemiols (named here as <i>α</i>-gersemiene), a recently discovered class of marine diterpenoid natural products.</p>

Terpene Tail-to-Head Polycyclization Mediated by Small Molecule Catalysts: A Weakly-Coordinating Anion Approach

<p>Biomimetic total synthesis has played a pivotal role in the development of synthetic organic chemistry. In particular, efforts aimed at mimicking the head-to-tail (HT) cation–π cyclization cascades invoked in terpene biosynthesis, such as those catalyzed by type-II cyclases, have led to a multitude of new synthetic methods, chemical concepts, and total syntheses over the past century. Conversely, synthetic methodology that mimics tail-to-head (TH) cation–π cyclization cascades, mediated by Mg²⁺ type-I terpene cyclases, remains elusive in organic synthesis, despite key roles in the biosynthesis of privileged therapeutic molecules such as taxol and artemesinin. Here we report that Li⁺/weakly-coordinating anion (WCA) salts catalyze the TH polycyclization of linaloyl fluoride, leading to high-yielding mixtures of polycyclic terpene natural products including cedrenes, cadinadiene, epizonarene, and 𝛿-selinene. The examples reported herein are the first small molecule-catalyzed TH polycyclization reactions enabling the shortest (formal) total synthesis of (<i>±</i>)-artemisinin. Moreover we apply this strategy to the diterpene geranyllinaloyl fluoride, resulting in a two-step total synthesis of the tricyclic core of the gersemiols (named here as <i>α</i>-gersemiene), a recently discovered class of marine diterpenoid natural products.</p>

Terpene Tail-to-Head Polycyclization Mediated by Small Molecule Catalysts: A Weakly-Coordinating Anion Approach

<p>Biomimetic total synthesis has played a pivotal role in the development of synthetic organic chemistry. In particular, efforts aimed at mimicking the head-to-tail (HT) cation–π cyclization cascades invoked in terpene biosynthesis, such as those catalyzed by type-II cyclases, have led to a multitude of new synthetic methods, chemical concepts, and total syntheses over the past century. Conversely, synthetic methodology that mimics tail-to-head (TH) cation–π cyclization cascades, mediated by Mg²⁺ type-I terpene cyclases, remains elusive in organic synthesis, despite key roles in the biosynthesis of privileged therapeutic molecules such as taxol and artemesinin. Here we report that Li⁺/weakly-coordinating anion (WCA) salts catalyze the TH polycyclization of linaloyl fluoride, leading to high-yielding mixtures of polycyclic terpene natural products including cedrenes, cadinadiene, epizonarene, and 𝛿-selinene. The examples reported herein are the first small molecule-catalyzed TH polycyclization reactions enabling the shortest (formal) total synthesis of (<i>±</i>)-artemisinin. Moreover we apply this strategy to the diterpene geranyllinaloyl fluoride, resulting in a two-step total synthesis of the tricyclic core of the gersemiols (named here as <i>α</i>-gersemiene), a recently discovered class of marine diterpenoid natural products.</p>

Hungry for charge – how a beryllium scorpionate complex “eats” a weakly coordinating anion

We present the reaction of a tris(pyrazolyl) beryllium scorpionate (TpBe) complex with a weakly coordinating anion (WCA), which yields the heteroleptic complex TpBeOC(CF3)31 (TpBeORF). The product 1 has been characterized by multinuclear NMR spectroscopy (1H, 9Be, 13C) and single-crystal X-ray diffraction (scXRD). Quantum chemical calculations (DFT, NPA, LOL) were performed to study the bonding nature in 1.

Al(ORF)3 (RF = C(CF3)3) activated silica: a well-defined weakly coordinating surface anion

A strong Lewis acid coordinates to silanols on silica to form a strong acid, which acts as a weakly coordinating anion when deprotonated.

Two heads are better than one: improving magnetic relaxation in the dysprosium metallocene upon dimerization by use of an exceptionally weakly-coordinating anion

Combining two weakly-coordinating anions in the archetypical metallocene results in the first example of [BPh4]− as a bridging ligand in 4f metals, resulting in improved magnetic relaxation dynamics over its mononuclear counterpart.