Synthetic and theoretical studies on group-transfer imidoylation of organotellurium compounds. remarkable reactivity of isonitriles in comparison with carbon monoxide in radical-mediated reactions

Controlled Radical Polymerization of Acrylates and Isocyanides Installs Degradable Functionality into Novel Copolymers

Installing ketones into a polymer backbone is a known method for introducing photodegradability into polymers; however, most current methods are limited to ethylene-carbon monoxide copolymerization. Here we use isocyanides in place of carbon monoxide in a copolymerization strategy to access degradable nonalternating poly(ketones) that either maintain or enhance the thermal properties. A cobalt-mediated radical polymerization of acrylates and isocyanides synthesizes nonalternating poly(acrylate-co-isocyanide) copolymers with tunable incorporation using monomer feed ratios. The kinetic product of the polymerization is a dynamic β-imine ester that tautomerizes to the β-enamine ester. Hydrolysis of this copolymer affords a third copolymer microstructure─the elusive nonalternating poly(ketone)─from a single copolymerization strategy. Analysis of the copolymer properties demonstrates tunable thermal properties with the degree of incorporation. Finally, we show that poly(acrylate-co-isocyanide) and poly(acrylate-co-ketone) are photodegradable with 390 nm light, enabling chain cleavage.

Isocyanide-Based Multicomponent Reactions Promoted by Visible Light Photoredox Catalysis

Isocyanide-based multicomponent reactions claim a one century-old history of flourishing developments. On the other hand, the enormous impact of recent progresses in visible light photocatalysis has boosted the identification of new straightforward and green approaches to both new and known chemical entities. In this context, the application of visible light photocatalytic conditions to multicomponent processes has been promoting key stimulating advancements. Spanning from radical-polar crossover pathways, to photoinduced and self-catalyzed transformations, to reactions involving the generation of imidoyl radical species, the present literature analysis would provide a general and critical overview about the potentialities and challenges of exploiting isocyanides in visible light photocatalytic multicomponent reactions.

Generation of (amino)(boryloxy)carbenes from carbamoylboranes and their coupling reaction with aldehydes

Carbamoylboranes were found to react with various aldehydes under heating conditions to give α-hydroxycarboxamides in good yields. A DFT study supports the mechanism, which involves thermally generated (amino)(boryloxy)carbene intermediates. To our knowledge, this is the first report on the generation of (amino)(boryloxy)carbene intermediates from carbamoylboranes and its application to carbon-carbon bond-forming reactions.

Acyl metalloids: conformity and deviation from carbonyl reactivity

Once considered as mere curiosities, acyl metalloids are now recognized for their utility in enabling chemical synthesis. This perspective considers the reactivity displayed by acylboron, -silicon, -germanium, and tellurium species. By highlighting the role of these species in various transformations, we demonstrate how differences between the comprising elements result in varied reaction outcomes. While acylboron compounds are primarily used in polar transformations, germanium and tellurium species have found utility as radical precursors. Applications of acylsilanes are comparatively more diverse, owing to the possibility to access both radical and polar chemistry.

Spectroscopic identification of the phenyltelluryl radical and its reactivity toward molecular oxygen

The phenyltelluryl radical was prepared by high-vacuum flash pyrolysis of diphenyl ditelluride and was chacracterized by matrix isolation IR and UV/Vis spectroscopy. After doping the matrix with molecular oxygen and allowing bimolecular reactions, the hitherto unkown phenyltelluro peroxy radical formed and was identified via IR spectroscopy. Irradiation with light at λ = 436 nm leads to isomerization to the thermodynamically more stable novel phenyltelluroyl radical. All experimental findings agree well with density functional theory (UB3LYP/Def2QZVPP and UM06-2X/Def2QZVPP) computations.

Isonitriles as Stereoelectronic Chameleons: The Donor-Acceptor Dichotomy in Radical Additions

Radical addition to isonitriles (isocyanides) starts and continues all the way to the transition state (TS) mostly as a simple addition to a polarized π-bond. Only after the TS has been passed, the spin density moves to the α-carbon to form the imidoyl radical, the hallmark intermediate of the 1,1-addition-mediated cascades. Addition of alkyl, aryl, heteroatom-substituted, and heteroatom-centered radicals reveals a number of electronic, supramolecular, and conformational effects potentially useful for the practical control of isonitrile-mediated radical cascade transformations. Addition of alkyl radicals reveals two stereoelectronic preferences. First, the radical attack aligns the incipient C···C bond with the aromatic π-system. Second, one of the C-H/C-C bonds at the radical carbon eclipses the isonitrile N-C bond. Combination of these stereoelectronic preferences with entropic penalty explains why the least exergonic reaction (addition of the t-Bu radical) is also the fastest. Heteroatomic radicals reveal further unusual trends. In particular, the Sn radical addition to the PhNC is much faster than addition of the other group IV radicals, despite forming the weakest bond. This combination of kinetic and thermodynamic properties is ideal for applications in control of radical reactivity via dynamic covalent chemistry and may be responsible for the historically broad utility of Sn radicals ("the tyranny of tin"). In addition to polarity and low steric hindrance, radical attack at the relatively strong π-bond of isonitriles is assisted by "chameleonic" supramolecular interactions of the radical center with both the isonitrile π*-system and lone pair. These interactions are yet another manifestation of supramolecular control of radical chemistry.

Silver-mediated radical coupling reaction of isocyanides and alcohols/phenols in the presence of water: unprecedented hydration and radical coupling reaction sequence

The first radical coupling of isocyanides and alcohols/phenols promoted by silver in the presence of water is reported.

Visible-Light-Induced Trifluoromethylation of Isonitrile-Substituted Methylenecyclopropanes: Facile Access to 6-(Trifluoromethyl)-7,8-Dihydrobenzo[k]phenanthridine Derivatives

A new visible-light-induced trifluoromethylation of isonitrile-substituted methylenecyclopropanes is developed. A range of substituted 6-(trifluoromethyl)-7,8-dihydrobenzo[k]phenanthridine derivatives are readily furnished by this newly developed tandem reaction with moderate to good yields. This reaction allows the direct formation of two six-membered rings and three new C-C bonds, including the C-CF3 bond, under visible light irradiation.

Light-Controlled Radical Polymerization: Mechanisms, Methods, and Applications

The use of light to mediate controlled radical polymerization has emerged as a powerful strategy for rational polymer synthesis and advanced materials fabrication. This review provides a comprehensive survey of photocontrolled, living radical polymerizations (photo-CRPs). From the perspective of mechanism, all known photo-CRPs are divided into either (1) intramolecular photochemical processes or (2) photoredox processes. Within these mechanistic regimes, a large number of methods are summarized and further classified into subcategories based on the specific reagents, catalysts, etc., involved. To provide a clear understanding of each subcategory, reaction mechanisms are discussed. In addition, applications of photo-CRP reported so far, which include surface fabrication, particle preparation, photoresponsive gel design, and continuous flow technology, are summarized. We hope this review will not only provide informative knowledge to researchers in this field but also stimulate new ideas and applications to further advance photocontrolled reactions.

Et3B-mediated two- and three-component coupling reactions via radical decarbonylation of α-alkoxyacyl tellurides: single-step construction of densely oxygenated carboskeletons

We devised new radical-based two- and three-component coupling reactions of sugar derivatives, and realized one-step construction of contiguously substituted polyol structures.

The single-step construction of various densely oxygenated carboskeletons was achieved by radical-based two- and three-component coupling reactions of sugar derivatives, without the need for light or heat. Et₃B/O₂-mediated decarbonylation readily converted α-alkoxyacyl tellurides to α-alkoxy carbon radicals, which intermolecularly added to glyoxylic oxime ether or enones to provide the two-component adducts. Furthermore, the three-component adducts were produced by an intermolecular aldol reaction between the aldehyde and the boron enolates generated by capture of the two-component radical intermediates by Et₃B. This powerful coupling method serves as a novel strategy for the convergent synthesis of polyol natural products.

Mn(ii)/O2-promoted oxidative annulation of vinyl isocyanides with boronic acids: synthesis of multi-substituted isoquinolines

An efficient manganese(ii)/O₂-promoted oxidative radical cascade reaction was developed for the modular synthesis of multi-substituted isoquinolines from easily accessible vinyl isocyanides and boronic acids.

1-Trifluoromethylated isoquinolines via radical trifluoromethylation of isonitriles

A simple and efficient approach to biologically important 1-trifluoroalkylated isoquinolines starting with readily prepared β-aryl-α-isocyano-acrylates and R_f-I(iii)-reagents (R_f = CF₃, C₂F₅, C₃F₇) is described.

An ab initio and DFT study of some halogen atom transfer reactions from alkyl groups to acyl radical

Ab initio calculations using the 6-311G**, cc-pVDZ, and (valence) double-zeta pseudopotential (DZP) basis sets, with (MP2, QCISD, CCSD(T)) and without (HF) the inclusion of electron correlation, and density functional (BHandHLYP, B3LYP) calculations predict that the transition states for the reaction of acetyl radical with several alkyl halides adopt an almost collinear arrangement of attacking and leaving radicals at the halogen atom. Energy barriers (DeltaE(double dagger)) for these halogen transfer reactions of between 89.2 (chlorine transfer from methyl group) and 25.3 kJ mol(-1) (iodine transfer from tert-butyl group) are calculated at the BHandHLYP/DZP level of theory. While the difference in forward and reverse energy barriers for iodine transfer to acetyl radical is predicted to be 15.1 kJ mol(-1) for primary alkyl iodide, these values are calculated to be 6.7 and -4.2 kJ mol(-1) for secondary and tertiary alkyl iodide respectively. These data are in good agreement with available experimental data in that atom transfer radical carbonylation reactions are sluggish with primary alkyl iodides, but proceed smoothly with secondary and tertiary alkyl iodides. These calculations also predict that bromine transfer reactions involving acyl radical are also feasible at moderately high temperature.

Microwave-Assisted Group-Transfer Cyclization of Organotellurium Compounds

Primary- and secondary-alkyl aryl tellurides, prepared by arenetellurolate ring-opening of epoxides/ O-allylation, were found to undergo rapid (3-10 min) group-transfer cyclization to afford tetrahydrofuran derivatives in 60-74% yield when heated in a microwave cavity at 250 degrees C in ethylene glycol or at 180 degrees C in water. To go to completion, similar transformations had previously required extended photolysis in refluxing benzene containing a substantial amount of hexabutylditin. The only drawback of the microwave-assisted process was the loss in diastereoselectivity which is a consequence of the higher reaction temperature. Substitution in the Te-aryl moiety of the secondary-alkyl aryl tellurides (4-OMe, 4-H, 4-CF(3)) did not affect the outcome of the group-transfer reaction in ethylene glycol. However, at lower temperature, using water as a solvent, the CF(3) derivative failed to react. The microwave-assisted group-transfer cyclization was extended to benzylic but not to primary- and secondary-alkyl phenyl selenides.