LongLarf

Nature, Published online: 06 November 2019; doi:10.1038/s41586-019-1681-6

Nature Communications, Published online: 08 November 2019; doi:10.1038/s41467-019-13072-x

Highly electron‐rich phosphines decorated with 1‐alkylpyridinylidenamino substituents (PyAPs) are accessible in one or two steps starting from inexpensive commercially available aminopyridines and chlorophosphines. The most basic PyAPs were used for the reversible CO₂ fixation and the formation of electron‐rich metal complexes relevant to catalysis.

Abstract

Electron‐rich tertiary phosphines are valuable species in chemical synthesis. However, their broad application as ligands in catalysis and reagents in stoichiometric reactions is often limited by their costly synthesis. Herein, we report the synthesis and properties of a series of phosphines with 1‐alkylpyridin‐4‐ylidenamino and 1‐alkylpyridin‐2‐ylidenamino substituents that are accessible in a very short and scalable route starting from commercially available aminopyridines and chlorophosphines. The determination of the Tolman electronic parameter (TEP) value reveals that the electron donor ability can be tuned by the substituent pattern at the aminopyridine backbone and it can exceed that of common alkylphosphines and N‐heterocyclic carbenes. The potential of the new phosphines as strong nucleophiles in phosphine‐mediated transformations is demonstrated by the formation of Lewis base adducts with CO₂ and CS₂. In addition, the coordination chemistry of the new phosphines towards Cu^I, Au^I, and Pd^II metal centers has been explored, and a convenient procedure to introduce the most basic phosphine into metal complexes starting from air‐stable phosphonium salt is described.

Synthetic approaches to fluorinated azides (with emphasis on α,α‐difluorinated azidoalkanes), their properties, stability and transformations are reviewed.

Abstract

Organic α‐fluorinated azidoalkanes appeared in the literature for the first time half a century ago. However, for a long time they remained undeveloped and were regarded as chemical curiosities. Recent advances in the preparation of α‐fluorinated azidoalkanes as well as studies on their stability and reactivity opened up their broader synthetic potential for the preparation of valuable fluorinated and non‐fluorinated compounds.

Herein we report a one‐pot protocol for the oxodealkenylative introduction of carbonyl functionalities into terpenes and terpene‐derived compounds. This transformation proceeds via Criegee ozonolysis of an alkene, reductive cleavage of the resulting α‐alkoxy hydroperoxide, trapping of the generated alkyl radical with TEMPO, and subsequent oxidative fragmentation with MMPP. Using readily available starting materials from chiral pool, a variety of carbonyl‐containing products have been accessed rapidly in good yields.

High‐lying SOMO radicals, generated in situ under visible‐light photoredox conditions, undergo an efficient addition to highly strained bicyclo[1.1.0]butanes, providing a straightforward access to valuable alkylated cyclobutanes.

Abstract

A new photoredox‐catalyzed decarboxylative radical addition approach to functionalized cyclobutanes is described. The reaction involves an unprecedented formal Giese‐type addition of C(sp³)‐centered radicals to highly strained bicyclo[1.1.0]butanes. The mild photoredox conditions, which make use of a readily available and bench stable phenyl sulfonyl bicyclo[1.1.0]butane, proved to be amenable to a diverse range of α‐amino and α‐oxy carboxylic acids, providing a concise route to 1,3‐disubstituted cyclobutanes. Furthermore, kinetic studies and DFT calculations unveiled mechanistic details on bicyclo[1.1.0]butane reactivity relative to the corresponding olefin system.

Nucleophilic substitutions (S _N ) are of fundamental importance. Especially in the recent years, catalysis has enabled significant advances towards more versatile and sustainable approaches for S _N ‐transformations. The current review summarises modern concepts for catalytic S _N ‐reactions and presents novel Lewis base promoted methods critically.

Nucleophilic substitutions (S _N ) account for the most essential and frequently applied chemical transformations. S _N ‐reactions allow forging C–C, C–O, C–N and C–Cl bonds, for example, from natural abundant starting materials such as alcohols and carboxylic acids. Products of S _N ‐reactions are ubiquitous and find inter alia applications as pharmaceuticals, plant protection agents and polymers. However, conventional S _N ‐type approaches are restricted frequently by the necessity of hazardous reagents and by‐products, a poor waste‐balance and therefore sustainability and high levels of costs, which especially impedes application in large scale synthesis. In order to provide solutions to these limitations, the development of novel catalytic methods for S _N ‐transformations has evolved into a flourishing and reviving area of research. The current review enables an overview of modern strategies for catalytic nucleophilic substitutions, presents as main topic the state‐of‐the‐art with respect to S _N ‐methods that are promoted by Lewis bases and points out potential future directions for further innovations.

Enhanced CO₂ transformation: The photocatalytic incorporation of CO₂ and iodo moieties into exo‐iodomethylene oxazolidinone proceeds efficiently, thereby offering a potential toolbox for organic synthesis using CO₂ with renewable energy to circumvent energy challenges in this field.

Abstract

A visible‐light‐promoted metal‐free carboxylative cyclization of propargylic amines with CO₂ was shown to offer exo‐iodomethylene 2‐oxazolidinones. Incorporation of both CO₂ and iodo moieties into these compounds was realized efficiently. The mechanism study revealed that this carboxylative cyclization proceeds through a radical pathway. Notably, the iodine‐functionalized 2‐oxazolidinone as a platform molecule could be easily converted into a wide range of value‐added chemicals through Buchwald–Hartwig, Suzuki, Sonogashira, photocatalytic ene, and photoreduction reactions. As a result, the plentiful downstream transformations remarkably enhance the range of chemicals derived from CO₂ and open a potential avenue for CO₂ functionalization to circumvent energy challenges in this field.

Abstract

4‐Methoxy‐3‐(trimethylphosphonio)phenolate was obtained from a regioselective addition of PMe₃ to p‐quinone monoacetal. This compound undergoes hydrogen isotope exchange with D₂O or CD₃CN, and is capable of catalyzing H/D exchange of CD₃CN with substrates bearing weakly acidic hydrogens. It exhibits similar reactivity to phosphorus ylides for olefinations of aldehydes. A possible tautomerization between the phosphonium phenolate zwitterion and phosphonium ylide is proposed for the first time to rationalize the unique reactivity.

Nature, Published online: 30 October 2019; doi:10.1038/s41586-019-1724-z