Preparation and Reactions of Mono- and Bis-Pivaloyloxyzinc Acetylides

The 12-Ethynylmonocarba-closo-dodecaborate Anion: A Ligand for Metal Alkynide Complexes (M = Li, Na, Ca, Zn)

We report the first isolation of metal alkynide complexes (2a-d) incorporating lithium, sodium, calcium and zinc based on the monocarborane endo/exo-dianionic framework [CB11H11-12-C≡C]2-. These complexes are synthesized via the deprotonation of terminal alkynes and optimized using lithium, sodium, calcium, and zinc hexamethyldisilazide bases to achieve enhanced yields and crystal stability. X-ray crystallography and NMR spectroscopy reveal unique coordination geometries, including a rare chair-shaped Li4C2O2 unit in 2a, multinuclear units in 2b-c, and a hexagonal Zn3C3 unit in 2d. Subsequent nucleophilic reactions with benzophenone afford propargylic alcohols (3) with high efficiency, demonstrating their utility in selective synthetic routes for complex molecular assembly. This work not only highlights the reactivity of alkali and alkaline-earth metals in monocarborane metal acetylides but also offers valuable insights into their structural characteristics and potential applications in advanced materials and catalytic systems.

Design and synthesis of 3,3'-triazolyl biisoquinoline N,N'-dioxides via Hiyama cross-coupling of 4-trimethylsilyl-1,2,3-triazoles

A new strategy to effectively lock the conformation of substituents at the 3,3'-positions of axial-chiral biisoquinoline N,N'-dioxides was developed based on the strong dipole-dipole interaction between 1,2,3-triazole and pyridine N-oxide rings. The crystal structure and the DFT calculations of 3,3'-bis(1-benzyl-1H-1,2,3-triazole-4-yl)-1,1'-biisoquinoline N,N'-dioxide (3a) provided strong support for this strategy. Furthermore, we successfully demonstrated that readily available 4-trimethylsilyl-1,2,3-triazoles are viable nucleophiles for Hiyama cross-coupling.

Organozinc pivalates for cobalt-catalyzed difluoroalkylarylation of alkenes

Installation of fluorine into pharmaceutically relevant molecules plays a vital role in their properties of biology or medicinal chemistry. Direct difunctionalization of alkenes and 1,3-dienes to achieve fluorinated compounds through transition-metal catalysis is challenging, due to the facile β-H elimination from the Csp³‒[M] intermediate. Here we report a cobalt-catalyzed regioselective difluoroalkylarylation of both activated and unactivated alkenes with solid arylzinc pivalates and difluoroalkyl bromides through a cascade Csp³‒Csp³/Csp³‒Csp² bond formation under mild reaction conditions. Indeed, a wide range of functional groups on difluoroalkyl bromides, olefins, 1,3-dienes as well as (hetero)arylzinc pivalates are well tolerated by the cobalt-catalyst, thus furnishing three-component coupling products in good yields and with high regio- and diastereoselectivity. Kinetic experiments comparing arylzinc pivalates and conventional arylzinc halides highlight the unique reactivity of these organozinc pivalates. Mechanistic studies strongly support that the reaction involves direct halogen atom abstraction via single electron transfer to difluoroalkyl bromides from the in situ formed cobalt(I) species, thus realizing a Co(I)/Co(II)/Co(III) catalytic cycle.

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

A cobalt-catalyzed acylation reaction of (hetero)arylzinc pivalates using primary, secondary and tertiary alkyl, benzyl and (hetero)aryl S-pyridyl thioesters has been developed.

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.

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.