Ni/Cu-Catalyzed Decarboxylative Addition of Alkynoic Acids to Terminal Alkynes for the Synthesis of gem-1,3-Enynes

Unlocking Diverse π-Bond Enrichment Frameworks by the Synthesis and Conversion of Boronated Phenyldiethynylethylenes

The π-bond enrichment frameworks not only serve as a crucial building block in organic synthesis but also assume a pivotal role in the fields of materials science, biomedicine, photochemistry, and other related disciplines owing to their distinctive structural characteristics. The incorporation of various substituents into the C═C double bonds of tetrasubstituted alkenes is currently a highly significant research area. However, the synthesis of tetrasubstituted alkenes with diverse substituents on double bonds poses a significant challenge in achieving stereoselectivity. Here, we reported an efficient and convergent route of Cu-catalyzed borylalkynylation of both symmetrical and unsymmetrical 1,3-diynes, B2pin2, and acetylene bromide to the construction of boronated phenyldiethynylethylene (BPDEE) derivatives with excellent chemo-, stereo-, and regioselectivities. BPDEE derivatives could transform into novel tetrasubstituted organic π-conjugated gem-diphenyldiethynylethylene (DPDEE), vinylphenyldiethynylethylene (VPDEE), and phenyltriethynylethylene (PTEE) derivatives by a stepwise process, which provides a flexible platform for the synthesis of complex π-bond enrichment frameworks that were difficult to synthesize by previous methods. The initial optical characterization revealed that the synthesized molecules exhibited aggregation-induced emission (AIE) properties, which further establishes the groundwork for future applications and enriches and advances the field of functional π-conjugated frameworks research.

Chemodivergent Synthesis of Oxazolidin-2-ones via Cu-Catalyzed Carboxyl Transfer Annulation of Propiolic Acids with Amines

Carboxylic acids are widely found in natural products and bioactive molecules and have served as raw material compounds in industry. We now report the first example of copper(I)-catalyzed carboxyl transfer annulation of propiolic acids with amines, thereby chemodivergently constructing the oxazolidine-2-ones. In this reaction, two kinds of key propargyamine intermediates were formed through sequential CuI/NBS-catalyzed oxidative deamination/decarboxylative alkynylation or CuI-catalyzed decarboxylative hydroamination/alkynylation. The advantages of this decarboxylative coupling/carboxylative cyclization are showcased in the atom economy, chemical specificity, and functional group tolerance.

Decarboxylative Addition of Propiolic Acids with Indoles to Synthesize Bis(indolyl)methane Derivatives with a Pd(II)/LA Catalyst

Exploring new protocols for efficient organic synthesis is crucial for pharmaceutical developments. The present work introduces a Pd(II)/LA-catalyzed (LA: Lewis acid) decarboxylative addition reaction for the synthesis of bis(indolyl)methane derivatives. The presence of Lewis acid such as Sc(OTf)₃ triggered Pd(II)-catalyzed decarboxylative addition of propiolic acids with indoles to offer the bis(indolyl)methane derivatives in moderate to good yields, whereas neither Pd(II) nor Lewis acid alone was active for this synthesis. The catalytic efficiency of Pd(OAc)₂ was highly dependent on the Lewis acidity of the added Lewis acid, that is, a stronger Lewis acid provided a higher yield of the bis(indolyl)methane derivatives. Meanwhile, this Pd(II)/LA-catalyzed decarboxylative addition reaction showed good tolerance toward versatile electron-rich or -deficient substituents on the indole skeleton and on the benzyl ring of propiolic acids. The studies on the in situ ¹H NMR kinetics of this Pd(II)/Sc(III) catalysis disclosed the formation of a transient vinyl-Pd(II)/Sc(III) intermediate generated by the pyrrole addition to the alkynyl-Pd(II)/Sc(III) species after decarboxylation, which was scarcely observed before.

Palladium-catalyzed decarboxylative gem-selective addition of alkynoic acids to terminal alkynes

Alkynoic acids added to terminal alkynes to give gem-1,3-enynes with high selectivity and good yields. In addition, the reaction of alkynoic acids with propiolic acid provided the corresponding gem-1,3-enynes via double decarboxylation.