Visible light-driven Giese reaction with alkyl tosylates catalysed by nucleophilic cobalt.

The scope of the Giese reaction is expanded using readily available alkyl tosylates as substrates and nucleophilic cobalt(i) catalysts under visible-light irradiation. The reaction proceeds preferentially with less bulky primary alkyl tosylates. This unique reactivity enables the regio-selective Giese reaction of polyol derivatives.

Reductive amidation of alkyl tosylates with isocyanates by a Ni/Co-dual catalytic system.

Reductive amidation of alkyl tosylates with isocyanates using the Ni/Co-dual catalytic system is disclosed. The method proceeds efficiently under mild conditions, giving rise to the corresponding alkyl amides. Notably, the protocol can discriminate the steric environment of two alkyl tosylate moieties, enabling regioselective mono-amidation at the less-bulky site.

Dithiazolylthienothiophene Bisimide: A Novel Electron-Deficient Building Unit for N-Type Semiconducting Polymers.

N-type (electron-transporting) semiconducting polymers are essential materials for the development of truly plastic electronic devices. Here, we synthesized for the first time dithiazolylthienothiophene bisimide (TzBI), as a new family for imide-based electron-deficient π-conjugated systems, and semiconducting polymers by incorporating TzBI into the π-conjugated backbone as the building unit. The TzBI-based polymers are found to have deep frontier molecular orbital energy levels and wide optical bandgaps compared to the dithienylthienothiophene bisimide (TBI) counterpart. It is also found that TzBI can promote the π-π intermolecular interactions of the polymer backbones relative to TBI most probably because the thiazole ring, which replaced the thiophene ring, at the end of the framework gives a more coplanar backbone. In fact, TzBI-based polymers function as the n-type semiconducting material in both organic field-effect transistor (OFET) and organic photovoltaic (OPV) devices. Notably, one of the TzBI-based polymers provides a power conversion efficiency of 3.3% in the all-polymer OPV device, which could be high for a low-molecular-weight polymer (<10 kDa). Interestingly, while many of the n-type semiconducting polymers utilized in OPVs have narrow bandgaps, the TzBI-based polymers have wide bandgaps. This is highly beneficial for complementing the visible to near-IR light absorption range when blended with p-type narrow bandgap polymers that have been widely developed in the last decade. The results demonstrate great promise and possibility of TzBI as the building unit for n-type semiconducting polymers.

Ni/Co-Catalyzed Homo-Coupling of Alkyl Tosylates.

A direct reductive homo-coupling of alkyl tosylates has been developed by employing a combination of nickel and nucleophilic cobalt catalysts. A single-electron-transfer-type oxidative addition is a pivotal process in the well-established nickel-catalyzed coupling of alkyl halides. However, the method cannot be applied to the homo-coupling of ubiquitous alkyl tosylates due to the high-lying σ*(C-O) orbital of the tosylates. This paper describes a Ni/Co-catalyzed protocol for the activation of alkyl tosylates on the construction of alkyl dimers under mild conditions.

Three-component coupling of aryl iodides, allenes, and aldehydes catalyzed by a Co/Cr-hybrid catalyst.

The cobalt/chromium-catalyzed three-component coupling of aryl iodides, allenes, and aldehydes has been developed to afford multi-substituted homoallylic alcohols in a diastereoselective manner. Control experiments for understanding the reaction mechanism reveal that the cobalt catalyst is involved in the oxidative addition and carbometalation steps in the reaction, whereas the chromium salt generates highly nucleophilic allylchromium intermediates from allylcobalt species, without the loss of stereochemical information, to allow the addition to aldehydes.

Nickel and Nucleophilic Cobalt-Catalyzed Trideuteriomethylation of Aryl Halides Using Trideuteriomethyl p-Toluenesulfonate.

Herein, a novel approach for the trideuteriomethylation of aryl halides using nickel and nucleophilic cobalt catalysts and the readily available trideuteriomethyl p-toluenesulfonate (CD3OTs) is described. This method provides access to a wide range of CD3-containing arenes. Moreover, a transmethylation step is revealed as crucial in the nickel/cobalt catalytic mechanism.

Nickel-Catalyzed Reductive Bis-Allylation of Alkynes.

A reductive nickel-catalyzed bis-allylation of alkynes with allyl acetates has been developed, leading to 1,4,7-triene skeletons. This reductive bis-allylation proceeds under mild conditions and exhibits good functional group tolerance in both the allyl acetates and the alkynes.

NHC-catalyzed cleavage of vicinal diketones and triketones followed by insertion of enones and ynones.

Thiazolium carbene-catalyzed reactions of 1,2-diketones and 1,2,3-triketones with enones and ynones have been investigated. The diketones gave α,ß-double acylation products via unique Breslow intermediates isolable as acid salts, whereas the triketones formed stable adducts with the NHC instead of the coupling products.

Highly nucleophilic vitamin B12-assisted nickel-catalysed reductive coupling of aryl halides and non-activated alkyl tosylates.

Reductive cross-coupling of aryl halides with ubiquitous alkyl tosylates was developed using a combination of nickel and vitamin B12 (VB12: cyanocobalamin) catalysts. The tosylate was activated by reduced VB12 to form alkyl cobalt(iii), which served as a good alkylating agent for aryl-nickel species, leading to C(sp3)-C(sp2) bond formation.

The drastic effect of cobalt and chromium catalysts in the borylation of arylzinc reagents.

A new synthetic approach to arylboronic esters from arylzinc reagents with boryl electrophiles MeOB(OR)2 has been developed. Furthermore, this protocol could be applied to the cyclization/borylation of alkynylaryl iodides to afford cyclized vinylboronic esters.

Practical Stannylation of Allyl Acetates Catalyzed by Nickel with Bu3 SnOMe.

A practical and scalable nickel-catalyzed allylic stannylation of allyl acetates with Bu3 SnOMe is described. A variety of acyclic and cyclic allyl acetates, even with base-sensitive moieties, undergoes the stannylation by using NiBr2 /4,4'-di-tert-butylbipyridine (dtbpy)/Mn catalyst system to afford highly functionalized allyl stannanes with excellent regioselectivity and yields. Furthermore, the scope of protocol is also extended by the reaction of propargyl acetates, giving rise to propargyl or allenyl stannanes. Additionally, a unique diastereoselectivity using the nickel catalyst different from the palladium was demonstrated for the stannylation of cyclic allyl acetates. In the reaction, inexpensive and stable nickel complexes, abundant reductant (Mn), and atom-economical stannyl source were used.

A Sn atom-economical approach toward arylstannanes: Ni-catalysed stannylation of aryl halides using Bu3SnOMe.

Stannylation of carbon-halogen bonds is one of the most promising and straightforward approaches for the preparation of organostannane compounds. Although a wide variety of methods are now available, all protocols require the use of highly nucleophilic organometals or wasteful stannyl sources like distannanes. Here, we report a new nickel-catalysed stannylation of aryl and alkenyl-halides using Bu3SnOMe as a stannyl source to afford aryl and vinyl-stannanes, respectively. This method enables the stannylation of not only bromides, but also chlorides and triflates to furnish functionalized aryl- and alkenyl-stannanes without the release of wasteful and toxic stannyl byproducts.

N-heterocyclic carbene-catalyzed double acylation of enones with benzils.

Thiazolium carbene-catalyzed reaction of aromatic 1,2-diketones with enones in aprotic solvents gave double acylation products in good yields, whereas hydroacylation products formed by Stetter reaction were not detected at all. These results suggested the generation of aroyloxyenamine species from the 1,2-diketones instead of hydroxyenamines (Breslow intermediates).

Cobalt-catalyzed formal [4+2] cycloaddition of α,α'-dichloro-ortho-xylenes with alkynes.

A formal [4+2] cycloaddition of α,α'-dichloro-ortho-xylenes with various alkynes has been developed using a low-valent cobalt catalyst. The transformation has a wide substrate scope and high functional-group tolerance and led to 1,4-dihydronaphthalenes. The formed cycloadducts were easily aromatized with MnO2 under air. A mechanistic investigation suggests that the transformation proceeds through a benzyl cobaltation of alkyne, not the classical Diels-Alder reaction of ortho-quinodimethanes. This methodology provides a straightforward and streamlined access to linearly expanded π-conjugated aromatics.

Borderline metal-catalyzed carboarylation of alkynylarenes using N,O-acetals.

Borderline metal catalysts, Bi(OTf)(3) and Fe(OTf)(3), were proven to work as dual activators for alkynes and N,O-acetals via σ,π-chelation, which achieved a new carboarylation reaction of alkynylarenes with N,O-acetals.

Tandem ene-reaction/hydroamination of amino-olefin and -allene compounds catalyzed by Bi(OTf)3.

Bi(OTf)(3) was proven to act as an effective catalyst for tandem ene-reaction/hydroamination of amino-olefin and amino-allene compounds with some enophiles, giving rise to functionalized N-heterocycles in good yields.

Cationic iron-catalyzed intramolecular alkyne-hydroarylation with electron-deficient arenes.

Fe(OTf)(3) effectively catalyzed intramolecular hydroarylation of aryl-substituted alkynes with electron-deficient arenes under mild conditions.

Bismuth-catalyzed intramolecular carbo-oxycarbonylation of 3-alkynyl esters.

Borderline metal complexes, especially Bi(OTf)3, efficiently catalyze the carbo-oxycarbonylation of alkynyl esters to form multisubstituted lactones in moderate to high yields.