A complementary approach to conjugated N-acyliminium formation through photoredox-catalyzed intermolecular radical addition to allenamides and allencarbamates

TCCA/RSeSeR-Mediated Selenoalkoxy of Allenamides via a Radical Process: Synthesis of Selanyl-allylic N,O-Aminals

An efficient TCCA (trichloroisocyanuric acid)/RSeSeR-mediated selenoalkoxy of allenamides for the construction of selanyl-allylic N,OA-aminal derivatives was developed. The reaction exhibits good functional group tolerance and high efficiency, affording the products in good to excellent yields. Mechanistic investigations indicated that a selanyl-allylic radical intermediate was first formed via the RSe radical added to the central carbon of allenamides, which subsequently furnished highly stable selanyl-allylic carbocation intermediate by abstraction of an electron by the chlorine radical. Moreover, this is the first report of using selenium reagent (RSeCl) to activate allenamides via a radical process.

Dehydrogenation Coupling and [3 + 2] Cycloaddition of Indolizines with Allenes in the Presence of Piezoelectric Materials under Ball Milling Conditions

A wide range of indolizines with allenes proceeded smoothly under mechanochemical-induced conditions via [3 + 2] annulation process, affording various substituted pyrrolo[2,1,5-cd]indolizines with good yield. The reaction efficiency was greatly improved by using a piezoelectric material as the charge transfer catalyst. The photophysical properties of the resulting pyrrolo[2,1,5-cd]indolizine was characterized.

Selective Hydrofunctionalization of N-Allenyl Derivatives with Heteronucleophiles Catalyzed by Brønsted Acids

In this study, we present a novel and environmentally sustainable protocol for the γ-hydrofunctionalization of N-allenyl compounds using various heteronucleophiles catalyzed solely by simple Brønsted acids. The method displays remarkable attributes, highlighting its sustainability, efficiency, regio- and stereoselectivity, as well as its versatile applicability to diverse heteroatom-containing enamides. Notably, our approach eliminates the need for metal catalysts and toxic solvents, representing a significant advancement in greener chemistry practices. We demonstrate the broad scope of our protocol by successfully scaling up reactions to gram-scale syntheses, underscoring its robustness for potential industrial implementation. The resulting γ-heterosubstituted enamides offer new possibilities for further synthetic transformations, yielding highly functionalized compounds with diverse applications. Mechanistic investigations reveal the pivotal role of CSA as a catalyst, enabling alcohol addition via a covalent activation mode.

Recent Progress in Free Radical Transformations of Allenamides

Allenamides are special allenes, and the unique reactivity, selectivity (both stereoselective and regionally selective) and stability of allenamides have been widely studied. In this review, the development of the free radical transformation of allenamides over the last few years will be summarized. This review discusses in detail in three parts: intermolecular radical addition to C- X (X = N, S, O, Se) bonds, metal salt mediated cyclization of allenamides, and photocatalytic cyclization of allenamides. In addition, reasonable details of the mechanisms are provided for the vast majority of these transformations.

PhI(OAc)2-Mediated Regioselective Hydrothiolation of Allenamides with Thiophenol via a Radical Process: Synthesis of Vinyl Sulfides

An efficient PhI(OAc)2-mediated regioselective hydrothiolation of allenamides with thiophenol via a radical process was developed to create a workable route to vinyl sulfides. The reaction exhibits a good functional group tolerance and high efficiency, affording the products in good to excellent yields. Mechanistic investigations indicated that the radical cascade proceeds through an allyl radical intermediate, which is formed via the addition of the PhS radical to the central carbon of allenamides. Moreover, the reaction was also efficient with selenophenol, providing the corresponding product, vinyl selenide, in a 99% yield.

Synthesis of 1,2-diselenides via potassium persulfate-mediated diselenation of allenamides with diselenides

An efficient potassium persulfate-mediated radical addition of allenamides with diselenides was developed to create a workable route to 1,2-diselenide products. The reaction tolerates a wide spectrum of functional groups to deliver the products in good to excellent yields. Mechanistic investigations including a calculation study indicated that the radical cascade proceeds through a vinyl radical intermediate, which is formed via a selenium radical added to the terminal CC double bond of allenamides.

Mechanochemically Induced Dehydrogenation Coupling and [3+2] Cycloaddition of Indolizines with Allenes Using Piezoelectric Materials

A wide range of indolizines with allenes proceeded smoothly under mechanochemically induced conditions via a [3+2] annulation process, affording various substituted pyrrolo[2,1,5-cd]indolizines in good yields. The reaction efficiency was greatly improved by using piezoelectric material as the charge transfer catalyst. The photophysical properties of the resulting pyrrolo[2,1,5-cd]indolizine were characterized.

Characterization and Utilization of the Elusive α,β-Unsaturated N-Tosyliminium: the Synthesis of Highly Functionalizable Skipped Halo Enynes

A formal haloalkynylation of allenamides has been described for the synthesis of highly stereo- and regioselective skipped halo enynes. Exclusive γ-regioselectivity is achieved through the intermediacy of a conjugated N-tosyliminium intermediate-direct evidence for the formation of which was validated by NMR and HRMS. Quantum mechanical computations reveal that the reactive intermediate geometry is key to controlling the 1,2- or 1,4-regioselectivity of alkyne interception. Divergent access to elusive unsaturated systems has also been reported.

Visible light mediated functionalization of allenes

This review summarizes the visible light mediated strategies for the functionalization of allenes.