Development of β,β-Dibrominated Secondary Enamides and Their Application to the Synthesis of 5-Br Oxazoles

Herein, we report a base promoted dibromination of enamides using CBr₄ as a bromine source to provide expedient access to β,β-dibrominated secondary enamides. Preliminary synthetic application study shows that these novel products can be readily transformed to 5-Br oxazoles via Cu(I) catalyzed intramolecular cyclization in good yields.

Tunable Lewis Basicity and Nucleophilicity of Water against α,α-Dihalo-β-acetoxyketones for the Selective Synthesis of α-Haloenones and 1,2-Diketones

The discovery and systematic study of tunable yet competitive nucleophilicity and Lewis basicity of water against novel building blocks α,α-dihalo-β-acetoxyketones (possessing a tertiary acetate) have been reported. This distinct reactivity resulted in the formation of two competitive and different products 1,2-diketones and α-haloenones from a common intermediate α,α-dihalo-β-acetoxyketones through the nucleophilicity and Lewis basicity of water, respectively. A systematic study to understand the effect of temperature and amount of water on the product distribution revealed that a lower temperature in combination with a higher amount of water shows a high preference for 1,2-diketones over α-haloenones. Measuring the dielectric constant (permittivity, ε) of various reaction media at various temperatures and a correlation with the experimental observations suggested that the reaction media with a higher dielectric constant exhibit the nucleophilic character and hence show a preference for 1,2-diketones over α-haloenones.

PIFA-Mediated Tandem Hofmann-Type Rearrangement and Cyclization Reaction of α-Acyl-β-aminoacrylamides: Access to Polysubstituted Oxazol-2(3H)-ones

An efficient and straightforward synthesis of polysubstituted oxazol-2(3H)-ones has been developed via a tandem Hofmann-type rearrangement and cyclization reaction of various α-acyl-β-aminoacrylamides mediated by phenyl iodine(III) bis(trifluoroacetate) (PIFA) in the presence of trifloroacetic acid (TFA). This novel protocol features readily available starting materials, mild reaction conditions, simple execution, high chemoselectivity, good functional group tolerance, and a metal-free oxidation process.

Haloamines as Bifunctional Reagents for Oxidative Aminohalogenation of Maleimides

An unprecedented copper-catalyzed oxidative aminohalogenation of electron-deficient maleimides with secondary amines and NXS (X = Cl, Br, I) was developed, in which the N-X bonds generated in situ were used as difunctionalized reagents. The distinctive features of this multicomponent reaction include a simple green catalytic system, a spectral substrate range, and the late-stage modification of drug molecules. Most importantly, this umpolung radical cascade strategy exploits the in situ formation of N-iodoamines that enable efficient alkene aminoiodination.

Synthesis of Sulfonamide-Based Ynamides and Ynamines in Water

Ynamides, though relatively more stable than ynamines, are still moisture-sensitive and prone to hydration especially under acidic and heating conditions. Here we report an environmentally benign, robust protocol to synthesize sulfonamide-based ynamides and arylynamines via Sonogashira coupling reactions in water, using a readily available quaternary ammonium salt as the surfactant.

Intermolecular Addition of Carbon-Centered Radicals to Ynamides. A Regio- and Stereoselective Route to Persubstituted α-Iodo-enamides

Rather surprisingly, C-C bond formation through "intermolecular" radical addition to internal ynamides has never been reported. Actually, ynamides are excellent acceptors for "electrophilic" carbon-centered radicals. These processes enable the introduction of functionalized alkyl chains at Cβ, groups that have not yet been introduced via the addition of organometallics. Radical carboiodination affords persubstituted α-iodo-enamides in moderate to high yield. The addition is totally stereoselective. Theoretical support to the mechanism and the scope and limitation of the reaction are discussed.

Practical Synthesis of Phosphinic Amides/Phosphoramidates through Catalytic Oxidative Coupling of Amines and P(O)-H Compounds

Herein, we report a highly efficient ZnI₂ -triggered oxidative cross-coupling reaction of P(O)-H compounds and amines. This operationally simple protocol provides unprecedented generic access to phosphinic amides/phosphoramidate derivatives in good yields and short reaction time. Besides, the reaction proceeds under mild conditions, which avoids the use of hazardous reagents, and is applicable to scale-up syntheses as well as late-stage functionalization of drug molecules. The stereospecific coupling is also achieved from readily available optically enriched P(O)-H compounds.

Transition-Metal-Free One-Step Synthesis of Ynamides

A robust transition-metal-free one-step strategy for the synthesis of ynamides from sulfonamides and ( Z)-1,2-dichloroalkenes or alkynyl chlorides is presented. This method is not only effective for internal ynamides but also amenable for terminal ynamides. Various functional groups, even the vinyl moiety, are compatible, and thus, this strategy offers the opportunity for further functionalization.

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.

Reactivity of epoxy-ynamides with metal halides: nucleophile (Br/Cl/OH)-assisted tandem intramolecular 5-exo-digor 6-endo-digcyclisation and AgF2-promoted oxidation

Several metal halides (CuBr, LiCl, CuF₂, AgF₂) react with epoxy-ynamides to afford 1,3-oxazolidines, 1,4-oxazines or 1,2-dioxo-enamides.

Enantioselective synthesis of β-amino acid derivatives via nickel-promoted regioselective carboxylation of ynamides and rhodium-catalyzed asymmetric hydrogenation

We succeeded in the development of a new method for enantioselective synthesis of α-substituted-β-amino acid derivatives. Thus, nickel(0)-promoted carboxylation of ynamide gave the α-substituted-β-aminoacrylate derivative in a highly regioselective manner. Then, rhodium-catalyzed asymmetric hydrogenation of the α-substituted β-aminoacrylate produced the corresponding α-substituted β-amino acid derivative as an optically active form.

PIFA-BF3·OEt2 mediated intramolecular regioselective domino cyclization of ynamides: A novel method for the synthesis of tetrahydroisoquinoline-oxazol-2(3H)-ones

The transition metal-free intramolecular regioselective domino cyclization of N-Boc protected ynamides has been developed to provide the corresponding tetrahydroisoquinoline-oxazo-2(3H)-ones in moderate to good yields.

Pd/Cu-Catalyzed tandem head-to-tail dimerization/cycloisomerization of terminal ynamides for the synthesis of 5-vinyloxazolones

This is the first Pd/Cu-catalyzed tandem head-to-tail dimerization/cycloisomerization of terminal ynamides for the synthesis of 5-vinyl-oxazolones.

Formation of α-chalcogenyl acrylamides through unprecedented chalcogen-mediated metal-free oxyfunctionalization of ynamides with DMSO as an oxidant

A novel chalcogen-mediated metal-free oxyfunctionalization mode of ynamides for the synthesis of α-chalcogenyl acrylamides has been developed.