Preparation of Primary and Secondary Dialkylmagnesiums by a Radical I/Mg-Exchange Reaction Using sBu2 Mg in Toluene.

The treatment of primary or secondary alkyl iodides with sBu2 Mg in toluene (25-40 °C, 2-4 h) provided dialkylmagnesiums that underwent various reactions with aldehydes, ketones, acid chlorides or allylic bromides. 3-Substituted secondary cyclohexyl iodides led to all-cis-3-cyclohexylmagnesium reagents under these exchange conditions in a highly stereoconvergent manner. Enantiomerically enriched 3-silyloxy-substituted secondary alkyl iodides gave after an exchange reaction with sBu2 Mg stereodefined dialkylmagnesiums that after quenching with various electrophiles furnished various 1,3-stereodefined products including homo-aldol products (99 % dr and 98 % ee). Mechanistic studies confirmed a radical pathway for these new iodine/magnesium-exchange reactions.

Facile Conversion of Molecularly Complex (Hetero)aryl Carboxylic Acids into Alkynes for Accelerated SAR Exploration.

1,2,3-Triazoles are well-established bioisosteres for amides, often installed as a result of structure-activity-relationship (SAR) exploration. A straightforward approach to assess the effect of the replacement of an amide by a triazole would start from the carboxylic acid and the amine used for the formation of a given amide and convert them into the corresponding alkyne and azide for cyclization by copper-catalyzed alkyne-azide cycloaddition (CuAAC). Herein, we report a functional-group-tolerant and operationally simple decarbonylative alkynylation that allows the conversion of complex (hetero)aryl carboxylic acids into alkynes. Furthermore, the utility of this method was demonstrated in the preparation of a triazolo analog of the commercial drug moclobemide. Lastly, mechanistic investigations using labeled carboxylic acid derivatives clearly show the decarbonylative nature of this transformation.

Directed regioselective ortho,ortho'-magnesiations of aromatics and heterocycles using sBu2Mg in toluene.

Aryl azoles are ubiquitous as bioactive compounds and their regioselective functionalization is of utmost synthetic importance. Here, we report the development of a toluene-soluble dialkylmagnesium base sBu2Mg. This new reagent allows mild and regioselective ortho-magnesiations of various N-arylated pyrazoles and 1,2,3-triazoles as well as arenes bearing oxazoline, phosphorodiamidate or amide directing groups. The resulting diarylmagnesium reagents were further functionalized either by Pd-catalyzed arylation or by trapping reactions with a broad range of electrophiles (aldehydes, ketones, allylic halides, acyl chlorides, Weinreb amides, aryl halides, hydroxylamine benzoates, terminal alkynes). Furthermore, several double ortho,ortho'-magnesiations were realized in the case of aryl oxazolines, N-aryl pyrazoles as well as 2-aryl-2H-1,2,3-triazoles by simply repeating the magnesiation/electrophile trapping sequence allowing the preparation of valuable 1,2,3-functionalized arenes.

Regioselective functionalization of aryl azoles as powerful tool for the synthesis of pharmaceutically relevant targets.

Aryl azole scaffolds are present in a wide range of pharmaceutically relevant molecules. Their ortho-selective metalation at the aryl ring is challenging, due to the competitive metalation of the more acidic heterocycle. Seeking a practical access to a key Active Pharmaceutical Ingredient (API) intermediate currently in development, we investigated the metalation of 1-aryl-1H-1,2,3-triazoles and other related heterocycles with sterically hindered metal-amide bases. We report here a room temperature and highly regioselective ortho-magnesiation of several aryl azoles using a tailored magnesium amide, TMPMgBu (TMP = 2,2,6,6-tetramethylpiperidyl) in hydrocarbon solvents followed by an efficient Pd-catalyzed arylation. This scalable and selective reaction allows variation of the initial substitution pattern of the aryl ring, the nature of the azole moiety, as well as the nature of the electrophile. This versatile method can be applied to the synthesis of bioactive azole derivatives and complements existing metal-mediated ortho-functionalizations.

Cobalt-Catalyzed Csp3-Csp3 Cross-Coupling of Functionalized Alkylzinc Reagents with Alkyl Iodides.

A mild cobalt-catalyzed Negishi-type cross-coupling of various functionalized dialkylzinc reagents with primary and secondary alkyl iodides in acetonitrile is reported using a combination of 20% CoCl2 and chelating nitrogen ligands. The method allows the construction of molecules with alkyl chains bearing sensitive functional groups at room temperature.

Potent hemithioindigo-based antimitotics photocontrol the microtubule cytoskeleton in cellulo.

Background: Hemithioindigo is a promising molecular photoswitch that has only recently been applied as a photoswitchable pharmacophore for control over bioactivity in cellulo. Uniquely, in contrast to other photoswitches that have been applied to biology, the pseudosymmetric hemithioindigo scaffold has allowed the creation of both dark-active and lit-active photopharmaceuticals for the same binding site by a priori design. However, the potency of previous hemithioindigo photopharmaceuticals has not been optimal for their translation to other biological models. Results: Inspired by the structure of tubulin-inhibiting indanones, we created hemithioindigo-based indanone-like tubulin inhibitors (HITubs) and optimised their cellular potency as antimitotic photopharmaceuticals. These HITubs feature reliable and robust visible-light photoswitching and high fatigue resistance. The use of the hemithioindigo scaffold also permitted us to employ a para-hydroxyhemistilbene motif, a structural feature which is denied to most azobenzenes due to the negligibly short lifetimes of their metastable Z-isomers, which proved crucial to enhancing the potency and photoswitchability. The HITubs were ten times more potent than previously reported hemithioindigo photopharmaceutical antimitotics in a series of cell-free and cellular assays, and allowed robust photocontrol over tubulin polymerisation, microtubule (MT) network structure, cell cycle, and cell survival. Conclusions: HITubs represent a powerful addition to the growing toolbox of photopharmaceutical reagents for MT cytoskeleton research. Additionally, as the hemithioindigo scaffold allows photoswitchable bioactivity for substituent patterns inaccessible to the majority of current photopharmaceuticals, wider adoption of the hemithioindigo scaffold may significantly expand the scope of cellular and in vivo targets addressable by photopharmacology.

Cobalt-Catalyzed Cross-Coupling of Functionalized Alkylzinc Reagents with (Hetero)Aryl Halides.

A combination of 10 % CoCl2 and 20 % 2,2'-bipyridine ligands enables cross-coupling of functionalized primary and secondary alkylzinc reagents with various (hetero)aryl halides. Couplings with 1,3- and 1,4-substituted cycloalkylzinc reagents proceeded diastereoselectively leading to functionalized heterocycles with high diastereoselectivities of up to 98:2. Furthermore, alkynyl bromides react with primary and secondary alkylzinc reagents providing the alkylated alkynes.

Cobalt-catalyzed acylation-reactions of (hetero)arylzinc pivalates with thiopyridyl ester derivatives.

A cobalt-catalyzed acylation reaction of various primary, secondary and tertiary alkyl, benzyl and (hetero)aryl S-pyridyl thioesters with (hetero)arylzinc pivalates is reported. The thioesters were prepared directly from the corresponding carboxylic acids under mild conditions, thus tolerating sensitive functional groups. Acylations of α-chiral S-pyridyl esters proceeded with very high stereoretention leading to optically enriched α-chiral ketones.

Hemithioindigos for Cellular Photopharmacology: Desymmetrised Molecular Switch Scaffolds Enabling Design Control over the Isomer-Dependency of Potent Antimitotic Bioactivity.

Druglike small molecules with photoswitchable bioactivity-photopharmaceuticals-allow biologists to perform studies with exquisitely precise and reversible, spatial and temporal control over critical biological systems inaccessible to genetic manipulation. The photoresponsive pharmacophores disclosed have been almost exclusively azobenzenes, which has limited the structural and substituent scope of photopharmacology. More detrimentally, for azobenzene reagents, it is not researchers' needs for adapted experimental tools, but rather protein binding site sterics, that typically force whether the trans (dark) or cis (lit) isomer is the more bioactive. We now present the rational design of HOTubs, the first hemithioindigo-based pharmacophores enabling photoswitchable control over endogenous biological activity in cellulo. HOTubs optically control microtubule depolymerisation and cell death in unmodified mammalian cells. Notably, we show how the asymmetry of hemithioindigos allows a priori design of either Z- or E- (dark- or lit)-toxic antimitotics, whereas the corresponding azobenzenes are exclusively lit-toxic. We thus demonstrate that hemithioindigos enable an important expansion of the substituent and design scope of photopharmacological interventions for biological systems.

Practical Ni-Catalyzed Cross-Coupling of Unsaturated Zinc Pivalates with Unsaturated Nonaflates and Triflates.

A practical nickel-catalyzed cross-coupling of (hetero)aryl or alkynylzinc pivalates with various unsaturated nonaflates or triflates is described. Organozinc pivalates allow these cross-couplings to take place with high yields and a low catalyst loading (0.5 mol %). Couplings with ( E)- and ( Z)-alkenyl triflates proceed with retention of configuration.

Cobalt-Catalyzed Diastereoselective Cross-Couplings between Alkynylzinc Pivalates and Functionalized Cyclic Iodides or Bromides.

Various 1,2-, 1,3-, and 1,4-substituted cyclic iodides or bromides undergo highly diastereoselective cross-couplings (diastereoselectivity (dr) up to 99:1) with a range of alkynylzinc pivalates, using CoCl2 (20 mol %) and trans- N, N, N', N'-tetramethylcyclohexane-1,2-diamine as a catalytic system.

A Robust and Broadly Applicable Cobalt-Catalyzed Cross-Coupling of Functionalized Bench-Stable Organozinc Pivalates with Unsaturated Halides.

We report a robust and broadly applicable CoCl2 -catalyzed cross-coupling between functionalized aryl and heteroaryl zinc pivalates and various electron-poor aryl and heteroaryl halides (X=Cl, Br, I). Couplings with (E)- or (Z)-bromo- or iodo-alkenes proceed with retention of configuration. Also, alkynyl bromides react with arylzinc pivalates providing arylated alkynes.

Mild Cobalt-Catalyzed Negishi Cross-Couplings of (Hetero)arylzinc Reagents with (Hetero)aryl Halides.

A catalytic system consisting of CoCl2 ⋅2 LiCl (5 mol %) and HCO2 Na (50 mol %) enables the cross-coupling of various N-heterocyclic chlorides and bromides as well as aromatic halogenated ketones with various electron-rich and -poor arylzinc reagents. The reactions reached full conversion within a few hours at 25 °C.