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A practical method for the synthesis of phenyl enol ethers is reported. The combination of a gold(I) catalyst and potassium carbonate selectively mediates the addition of phenols to propargylic alcohols/amines in a chemo-, regio-, and stereoselective fashion in high yield. The resulting enol ethers are formed exclusively with a Z-configuration and can be obtained from a wide array of phenols and propargylic alcohols or amines with the reaction showing excellent functional group tolerance.

Trisubstituted cyclic organic carbonates with multiple though well-defined stereochemical configurations are difficult to prepare. Here we present a conceptual design toward these CO2-based synthons using hydroxyl-substituted cyclic epoxide precursors and their catalytic conversion, to afford these challenging target compounds with fused ring sizes of up to eight under excellent stereocontrol. The observed stereochemistry of the organic carbonates combined with various control experiments revealed that these compounds are formed through a mechanistic manifold that involves a depolymerization reaction within an oligomeric carbonate induced by a pendant hydroxyl nucleophile. This manifold therefore provides an alternative approach toward CO2 valorization into functional cyclic carbonate scaffolds of use in synthetic chemistry.

A versatile approach to the valorization of propargylic alcohols is reported, enabling controlled access to three different products from the same starting materials. First, a general method for the hydroamination of propargylic alcohols with anilines is described using gold catalysis to give 3-hydroxyimines with complete regioselectivity. These 3-hydroxyimines can be reduced to give 1,3-amino alcohols with high syn selectivity. Alternatively, by using a catalytic quantity of aniline, 3-hydroxyketones can be obtained in high yield directly from propargylic alcohols. Further manipulation of the reaction conditions enables the selective formation of 3-aminoketones via a rearrangement/hydroamination pathway. The utility of the new chemistry was exemplified by the one-pot synthesis of a selection of N-arylpyrrolidines and N-arylpiperidines. A mechanism for the hydroamination has been proposed on the basis of experimental studies and density functional theory calculations.

Catalytic direct amidation reactions have been the focus of considerable recent research effort, due to the widespread use of amide formation processes in pharmaceutical synthesis. However, the vast majority of catalytic amidations are performed in non-polar solvents (aromatic hydrocarbons, ethers) which are typically undesirable from a sustainability perspective, and are often poor at solubilising polar carboxylic acid and amine substrates. As a consequence, most catalytic amidation protocols are unsuccessful when applied to polar and/or functionalised substrates of the kind commonly used in medicinal chemistry. In this paper we report a practical and useful catalytic direct amidation reaction using tert-butyl acetate as the reaction solvent. The use of an ester solvent offers improvements in terms of safety and sustainability, but also leads to an improved reaction scope with regard to polar substrates and less nucleophilic anilines, both of which are important components of amides used in medicinal chemistry. An amidation reaction was scaled up to 100 mmol and proceeded with excellent yield and efficency, with a measured process mass intensity of 8.

Aluminum(III) complexes derived from aminotriphenolate ligands are shown to be excellent catalysts for the formation of cyclic sulfites from a range of (functionalized) terminal and internal epoxides, and ex situ generated sulfur dioxide. The developed catalytic protocol is characterized by its operational simplicity, wide scope in epoxide reaction partners, good to excellent isolated yields and mild reaction conditions [50–70 °C, p(SO2)

A highly regioselective catalytic approach has been developed towards carbamates derived from cyclic organic carbonates by reaction of the latter with amine reagents under organocatalytic control. For various combinations of carbonate and amine substrates, an organocatalyst (TBD: 1,5,7-triazabicyclo[4.4.0]dec-5-ene) was used to increase the reaction kinetics while exerting excellent regioselective control. The current method is the first general approach towards the control over the regioselectivity of this reaction using a wide variety of easily accessed substituted organic carbonates.

An efficient and practical aluminium-catalysed approach towards a range of functional oxazolidinones is reported. The method is based on cheap and readily available starting materials including terminal and internal (bicyclic) epoxides and phenyl carbamate. The oxazolidinones serve as highly useful synthons for the high yield preparation of non-symmetrical ureas by nucleophilic ring-opening affording the targeted urea compounds with excellent functional group diversity, high regioselectivity and isolated yields up to >99%.

The efficient and highly selective formation of a wide range of (hetero)cyclic cis-diol scaffolds using powerful aminotriphenolate- based metal catalysts is reported. The key intermediates are cyclic carbonates that are derived in high yield and with high levels of diastereo- and chemo-selectivity from the parent oxirane precursors and carbon dioxide (CO2). Deprotection of the carbonate structures affords synthetically useful cis-diol scaffolds with different ring sizes incorporating various functional groups. This atom-efficient methodology allows for simple construction of diol synthons using cheap and accessible precursors and green metal catalysts, and showcases the use of CO2 as a temporary protecting group.

A broad spectrum of substituted carbonate substrates is subjected to aminolysis in the presence of TBD.

Oxetanes are versatile building blocks in drug-related synthesis to induce property-modulating effects. Whereas related oxiranes are widely used in coupling chemistry with carbon dioxide (CO2) to afford value-added commodity chemicals, oxetane/CO2 couplings remain extremely limited despite the recent advances in the synthesis of these four-membered heterocycles. Here we report an effective one-pot three-component reaction (3CR) strategy for the coupling of (substituted) oxetanes, amines and CO2 to afford a variety of functionalized carbamates with excellent chemoselectivity and good yields. The process is mediated by an aluminium-based catalyst under relatively mild conditions and the developed catalytic methodology can be applied to the formal synthesis of two pharmaceutically relevant carbamates with the 3CR being a key step.

Oxetanes are versatile building blocks in drug- related synthesis to induce property-modulating effects. Whereas related oxiranes are widely used in coupling chemistry with carbon dioxide (CO2) to afford value-added commodity chemicals, oxetanes/CO2 couplings remain extremely limited despite the recent advances in the synthesis of these four-membered heterocycles. Here we report an effective one-pot three-component reaction (3CR) strategy for the coupling of (substituted) oxetanes, amines and CO2 to afford a variety of functionalized carbamates with excellent chemo-selectivity and good yields. The process is mediated by an aluminium based catalysts under relatively mild conditions and the developed catalytic methodology can be applied to the formal synthesis of two pharmaceutically relevant carbamates with the 3CR being a key step.

This chapter describes in general terms the catalytic methodology that has been made available for the use of carbon dioxide (CO2) in cyclization reactions that incorporate an intact CO2 fragment without changing the formal oxidation state of the carbon center. The major focus of this chapter will be on the most successful organometallic/inorganic complexes that have been used as catalyst systems throughout the last decade, and the preferred ligand frameworks leading to elevated reactivity and/or selectivity behavior in CO2 coupling reactions. Attention will be especially given to homogeneous catalyst systems as they have proven to be more versatile in CO2 conversion catalysis, and often have modular characteristics that allow for optimization of structure-activity relationships. The most important reactions that have been studied in the current context are designated CO2 “addition” reactions to small molecule heterocycles such as epoxides and aziridines, though more recently other coupling partners such as diamines, dialcohols and amino-nitriles have further advanced the use of CO2 in organic synthesis providing access to a wider range of structures. This chapter will serve to demonstrate the utility of CO2 as a carbon reagent in the catalytic formation of the most prominent organic structures using cyclization strategies specifically.

Efficient procedures are described for the reaction of cyclic epoxides with carbon dioxide to give cyclic carbonates generally with exclusive or high cis-diastereoselectivity.

Al(III) complexes of amino-tris(phenolate) ligand scaffolds have been prepared to attain highly Lewis acidic catalysts. Combination of the aforementioned systems with ammonium halides provides highly active catalysts for the synthesis of organic carbonates through addition of carbon dioxide to oxiranes with initial turnover frequencies among the highest reported to date within the context of cyclic carbonate formation. Density functional theory (DFT) studies combined with kinetic data provides a rational for the relative high activity found for these Al(III) complexes, and the data are consistent with a monometallic mechanism. The activity and versatility of these Al(III) complexes has also been evaluated against some state-of-the-art catalysts and the combined results compare favorably in terms of catalyst construction, stability, activity, and applicability.

An aluminum complex based on an amino triphenolate ligand scaffold shows unprecedented high activity (initial TOFs up to 36 000 h–1), broad substrate scope, and functional group tolerance in the formation of highly functional organic carbonates prepared from epoxides and CO2. The developed catalytic protocol is further characterized by low catalyst loadings and relative mild reaction conditions using a cheap, abundant, and nontoxic metal.

An aluminum complex based on an amino triphenolate ligand scaffold shows unprecedented high activity (initial TOFs up to 36,000 h(-1)), broad substrate scope, and functional group tolerance in the formation of highly functional organic carbonates prepared from epoxides and CO(2). The developed catalytic protocol is further characterized by low catalyst loadings and relative mild reaction conditions using a cheap, abundant, and nontoxic metal.

Valorization of carbon dioxide into organic molecules using catalytic approaches has witnessed an upsurge in recent years. Here, the influence of an Al(III) aminotriphenolate complex on the regio- and stereo-chemical features of the coupling between carbon dioxide and a cyclic epoxy alcohol has been studied. Three distinct bicyclic carbonate products were produced from a single starting material depending on the catalytic conditions. The proposed carbonate configurations were examined by solution and solid phase techniques including NMR spectroscopic and X-ray crystallographic analyses. Control experiments combined with DFT calculations provide a rationale for the distinct catalytic manifolds observed in the presence and absence of the Al(III) complex.