HFIP-Mediated, Highly Chemo-, Regio-, and Stereoselective Hydrofunctionalizations of Ynamides: Access to Stereodefined Alkenes Bearing Drugs and Natural Products

We disclose a sustainable and versatile synthetic strategy for the highly chemo-, regio-, and stereoselective hydrofunctionalizations of ynamides, through its activation by a solvent, HFIP, to access a wide variety of stereodefined ketene N,N, N,O, N,S, and N,Se acetals in high yield at room temperature. The reaction proceeded through the formation of the reactive keteniminium ion intermediate, formed via protonation at the β-carbon of ynamide by HFIP, followed by an attack of a nucleophile (syn-addition) at the α-carbon. When ynamides are treated with only HFIP at room temperature, the HFIP addition products of ynamides are formed in a 100% atom-economic fashion; however, in the presence of a stronger N-/O-/S-/Se-based nucleophile, the corresponding syn-hydroheterofunctionalized products are formed. Notably, HFIP played multiple roles, such as a reagent, in particular, a Brønsted acid, nucleophile, as well as solvent. Interestingly, HFIP is found to be unique for this transformation. Notably, this strategy is utilized for the late-stage functionalization of several marketed drugs and natural products, and it also enables the connection of two different drugs or a drug and a natural product through chemical bonds. Significantly, HFIP was recovered after the reaction and reused for consecutive reactions.

Phosphine-catalyzed regio- and stereo-selective hydroboration of ynamides to (Z)-β-borylenamides

We report a tri-n-butyl phosphine catalyzed regio- and stereo-selective hydroboration of ynamides to yield (Z)-β-borylenamides in good yields. Surprisingly, a formal cis addition to the triple bond was observed as confirmed by NMR and X-ray crystallography. ³¹P NMR studies suggest that a zwitterionic vinylphosphonium intermediate is key in the mechanism. The resulting products were further transformed to β-CF₃ enamides via stereoretentive trifluoromethylation.

Copper-catalyzed radical trans-selective hydroboration of ynamides with N-heterocyclic carbene boranes

Vinylboron compounds are important compounds in organic chemistry and biology. In this communication, we developed a copper(I)-catalyzed, highly regio- and stereoselective radical trans-hydroboration of ynamides with N-heterocyclic carbene (NHC)-ligated borane is reported, which leads to a series of trans-boryl enmides that can be conveniently transformed into various multi-substituted enamides. Further investigation showcased that our method is robust and scalable. The mechanism of this unique reaction is studied and discussed.

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A Cu-catalyzed highly regio- and stereoselective radical trans-hydroboration of ynamides

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Good to excellent yields, good functional group tolerance

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Further investigation showcased that our method is robust and scalable

Enantioselective Rhodium-Catalyzed Hydrogenation of (Z)-N-Sulfonyl-α-dehydroamido Boronic Esters

Highly enantioselective rhodium-catalyzed hydrogenation of (Z)-N-sulfonyl-α-dehydroamido boronic esters is realized for the first time using a JosiPhos-type ligand. This method has enabled convenient synthesis of a series of enantio-enriched N-sulfonyl-α-amido boronic esters in good yields and excellent enantioselectivities (up to 99% ee).

Ligand-free, catalytic and regioselective hydroboration of selenoalkynes

The copper-catalyzed hydroboration of selenoalkynes in a regio- and stereoselective fashion is reported, delivering selenium-containing vinylboronate products in good yields.

Catalytic asymmetric hydrogenation of (Z)-α-dehydroamido boronate esters: direct route to alkyl-substituted α-amidoboronic esters

The direct catalytic asymmetric hydrogenation of (Z)-α-dehydroamino boronate esters was realized. Using this approach, a class of therapeutically relevant alkyl-substituted α-amidoboronic esters was easily synthesized in high yields with generally excellent enantioselectivities (up to 99% yield and 99% ee). The utility of the products has been demonstrated by transformation to their corresponding boronic acid derivatives by a Pd-catalyzed borylation reaction and an efficient synthesis of a potential intermediate of bortezomib. The clean, atom-economic and environment friendly nature of this catalytic asymmetric hydrogenation process would make this approach a new alternative for the production of alkyl-substituted α-amidoboronic esters of great potential in the area of organic synthesis and medicinal chemistry.

Preparation and Utility of N-Alkynyl Azoles in Synthesis

Heteroatom-substituted alkynes have attracted a significant amount of interest in the synthetic community due to the polarized nature of these alkynes and their utility in a wide range of reactions. One specific class of heteroatom-substituted alkynes combines this utility with the presence of an azole moiety. These N-alkynyl azoles have been known for nearly 50 years, but recently there has been a tremendous increase in the number of reports detailing the synthesis and utility of this class of compound. While much of the chemistry of N-alkynyl azoles mirrors that of the more extensively studied N-alkynyl amides (ynamides), there are notable exceptions. In addition, as azoles are extremely common in natural products and pharmaceuticals, these N-alkynyl azoles have high potential for accessing biologically important compounds. In this review, the literature reports of N-alkynyl azole synthesis, reactions, and uses have been assembled. Collectively, these reports demonstrate the growth in this area and the promise of exploiting N-alkynyl azoles in synthesis.

Efficient heterogeneous hydroboration of alkynes: enhancing the catalytic activity by Cu(0) incorporated CuFe2O4 nanoparticles

Nano-copper ferrite supported Cu catalysts are active for hydroboration of alkynes to vinylboronates.

Regiospecific and stereoselective synthesis of (E)- and (Z)-2-phosphino-1-alkenyl boronates via Cu-catalyzed hydroboration of alkynylphosphines

The regiospecific and stereoselective synthesis of (E)- and (Z)-2-phosphino-1-alkenyl boronates via Cu-catalyzed hydroboration of alkynylphosphines has been developed.

Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse

Although known for over 90 years, only in the past two decades has the chemistry of diboron(4) compounds been extensively explored. Many interesting structural features and reaction patterns have emerged, and more importantly, these compounds now feature prominently in both metal-catalyzed and metal-free methodologies for the formation of B-C bonds and other processes.

Copper-catalyzed hydroboration of propargyl-functionalized alkynes in water

The Cu-catalyzed hydroboration of alkynes in operationally simple and environmentally friendly conditions is reported.