α-Vinylation of Ester Equivalents via Main Group Catalysis for the Construction of Quaternary Centers

A methodology for the construction of sterically congested quaternary centers via the trapping of vinyl carbocations with silyl ketene acetals is disclosed. This main group-catalyzed α-vinylation reaction is advantageous as methods to access these congested motifs are limited. Moreover, β,γ-unsaturated carbonyl moieties and tetrasubstituted alkenes are present in various bioactive natural products and pharmaceuticals, and this catalytic platform offers a means of accessing them using simple and inexpensive materials.

Vinyl cation-mediated intramolecular hydroarylation of alkynes using pyridinium reagents

Once considered to be exotic species of limited synthetic utility, vinyl cations have recently been shown to be highly versatile intermediates in a variety of processes. Here, we report a method for the synthesis of aryl-substituted benzocycloheptenes and -hexenes using the hydrotriflate salt of an electron-poor pyridine as a uniquely efficient proton source for a vinyl cation mediated Friedel-Crafts cyclization. The mild conditions made possible by this reagent allowed a range of simple and functionalized alkynes bearing pendant aryl groups to serve as suitable substrates for this scalable and convenient protocol.

Unified Approach to Diverse Fused Fragments via Catalytic Dehydrative Cyclization

A range of highly functionalized polycyclic fragments have been synthesized, employing a catalytic dehydrative cyclization. A range of nucleophiles are shown to be successful, with the reaction producing numerous high value motifs.

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

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.

Iron-catalyzed carboarylation of alkynes via activation of π-activated alcohols: rapid synthesis of substituted benzofused six-membered heterocycles

An Fe(OTf)3-catalysed carboarylation of alkynes is reported for the straightforward synthesis of densely substituted 1,2-dihydroquinolines from N-propargyl anilides and π-activated alcohols. The reaction provides a new method for the synthesis of highly substituted benzofused six-membered heterocycles by the formation of two carbon-carbon bonds and one ring in a single step. The power of the methodology was further extended to the synthesis of substituted chromene and thiochromene derivatives in high yields. In addition, substituted quinoline derivatives were also achieved in a single step in the presence of FeCl3 through detosylation/aromatisation. A number of control experiments have been performed and a plausible mechanism has also been proposed to explain the formation of the products.

Vinyl and Alkynyl Triazenes: Synthesis, Reactivity, and Applications

Aromatic compounds containing triazenyl groups (N₃ RR') have a profound impact on synthetic organic and medicinal chemistry. In contrast, the chemistry of vinyl and alkynyl triazenes was a largely uncharted territory until recently. The situation has changed over the last five years, and it has become apparent that vinyl and alkynyl triazenes are highly interesting compounds with a unique reactivity. The electron-donating properties of the triazenyl group provide alkynyl triazenes with an ynamide-like reactivity, which can be exploited in reactions of the triple bond. Vinyl triazenes, on the other hand, can be used for electrophilic vinylation reactions. The foundation for this new triazene chemistry are synthetic pathways which allow preparing vinyl and alkynyl triazenes in few steps from readily available starting materials. In this Minireview, we summarize recent developments in this area.

Synthesis of Functionalized Isoindolinones via Calcium Catalyzed Generation and Trapping of N-Acyliminium Ions

Herein we report our full investigation into the calcium catalyzed generation and trapping of N-acyliminium ions from readily available 3-hydroxyisoindolinones. We have successfully employed a range of traditional nucleophiles including carbon, nitrogen, and sulfur containing reactive partners. The reaction is tolerant to a wide range of functionalities and provides high value scaffolds in good to excellent yields.

A Ba/Pd Catalytic System Enables Dehydrative Cross-Coupling and Excellent E-Selective Wittig Reactions

A Ba/Pd cooperative catalysis system was developed to enable the dehydrative cross-coupling of allylic alcohols with P-ylides to occur directly and promote a subsequent Wittig reaction in one pot. A variety of multisubstituted 1,4-dienes were isolated in good to excellent yields with broad P-ylides (stabilized by both ester and ketone carbonyl groups) and aldehyde (aliphatic and aromatic) substrates with excellent E selectivity.

Functionalisation of isoindolinones via a calcium catalysed Hosomi-Sakurai allylation

A rapid and functionally tolerant calcium catalysed Hosomi-Sakurai reaction has been realised. Employing 1 mol% calcium, allylated isoindolinones can be synthesised in high yields and the reaction is shown to be tolerant to a range of medicinally relevant functional groups including heterocycles. The synthetic utility of the reaction has been shown, and a plausible reaction mechanism is provided.

Nitration and Cyclization of Arene-Alkynes: An Access to 9-Nitrophenathrenes

A nitration and cyclization of arene-alkynes has been developed, affording 9-nitrophenathrenes efficiently. This reaction probably proceeds via addition of the nitrogen dioxide to the alkyne moiety, intramolecular radical addition of vinyl radical to one aryl ring, oxidation of radical intermediate into carbocation species, and elimination of a proton. In this transformation, Fe(NO₃)₃ was used as both nitro source and oxidant.

In(III)-TMSBr-Catalyzed Cascade Reaction of Diarylalkynes with Acrylates for the Synthesis of Aryldihydronaphthalene Derivatives

A combined Lewis acid system comprising of two or more Lewis acids occasionally exhibits augmented catalytic activity in organic transformations which are otherwise unrealizable by either of the components exclusively. On the other hand, the efficient construction of multiple new C-C bonds and polycyclic structures in minimal steps remains a subject of great interest in both academia and industry. Herein we report an efficient method to assemble aryldihydronaphthalene derivatives via a cascade reaction of diarylalkynes with acrylates under the catalysis of a combined Lewis acid derived from In(III) salt and TMSBr.

α-Carbonyl Cations in Sulfoxide-Driven Oxidative Cyclizations

The selective, metal-free generation of α-carbonyl cations from simple internal alkynes was accomplished by the addition of a sulfoxide to a densely substituted vinyl cation. The high reactivity of the α-carbonyl cations was found to efficiently induce hydrogen and even carbon shift reactions with unusual selecivities. Complex compounds with highly congested tertiary and all-carbon-substituted quartenary carbon centers can thus be accessed in a single step from simple precursors. Mechanistic analysis strongly supports the intermediacy of the title compounds and provides a simple predictive scheme for the migratory aptitude of different substituents.

Metal free carboamination of internal alkynes – an easy access to polysubstituted quinolines

A synergistic Brønsted acid catalyst was used to intermolecularly generate vinyl cations for a C–C bond formation – Schmidt rearrangement – sequence.

Ca(II) -catalyzed alkenylation of alcohols with vinylboronic acids

Direct alkenylation of a variety of alcohols with vinylboronic acids has been accomplished using the air-stable calcium(II) complex Ca(NTf2 )2 under mild conditions with short reaction times. For reluctant transformations, an ammonium salt was used as an additive to circumvent the reactivity issue.