SOMOphilic alkyne vs radical-polar crossover approaches: The full story of the azido-alkynylation of alkenes

We report the detailed background for the discovery and development of the synthesis of homopropargylic azides by the azido-alkynylation of alkenes. Initially, a strategy involving SOMOphilic alkynes was adopted, but only resulted in a 29% yield of the desired product. By switching to a radical-polar crossover approach and after optimization, a high yield (72%) of the homopropargylic azide was reached. Full insights are given about the factors that were essential for the success of the optimization process.

Nickel-Catalyzed Deaminative Alkyl-Alkyl Cross-Coupling of Katritzky Salts with Cyclopropanols: Merging C-N and C-C Bond Activation

Herein, we report a general and practical nickel-catalyzed deaminative alkylation of Katritzky salts with cyclopropyl alcohols via merging C-N and C-C bond activation. This protocol enables the formation of an alkyl-alkyl bond along with the generation of a versatile ketone functional group in a single operation, thus providing a convenient approach for accessing β-alkyl ketones. This reaction is distinguished by its high functional group tolerance, broad substrate scope, and efficient late-stage derivatization of complex bioactive molecules.

Enantioselective Synthesis of Isoindolinone by Palladium-Catalyzed Aminoalkynylation of O-Phenyl Hydroxamic Ethers with Alkynes

A highly efficient palladium-catalyzed asymmetric tandem aza-Heck/Sonogashira coupling reaction of O-phenyl hydroxamic ethers with terminal alkynes is described. This protocol enables versatile access to challenging chiral isoindolinone derivatives bearing a quaternary stereogenic center. The palladium-catalyzed aminoalkynylation reaction shows broad functional group tolerance and allows the straightforward preparation of isoindolinones with high efficiency and excellent enantioselectivity under mild conditions. DFT calculations were performed to disclose the reaction mechanism and the origins of the enantioselectivity.

Access to pyrrolines and fused diaziridines by selective radical addition to homoallylic diazirines

Pyrroline derivatives are common in bioactive natural products and therapeutic agents. We report here a synthesis of pyrrolines and fused diaziridines by divergent radical cyclization of homoallylic diazirines, which can serve as an internal radical trap and a nitrogen source. This reaction proceeds by selective radical addition to C[double bond, length as m-dash]C or N[double bond, length as m-dash]N bonds followed by intramolecular cyclization. Frontier molecular orbital analysis provides a deep insight into the origin of the selectivity. The reaction demonstrates a new cyclization mode, broad functional group compatibility and high product diversity, and reveals a much broader chemical space for diazirine studies.

Nickel-Catalyzed Reductive Iminoarylation of Oxime Ester-Tethered Alkenes: Rapid Entrance to Diverse Functionalized Pyrrolines

Herein, we disclose a general and practical iminoarylation of alkenes by nickel-catalyzed reductive cross-coupling of unsaturated oxime esters with readily available aryl halides, providing an expedient approach for constructing pyrroline derivatives. The absence of organometallic reagents enables the reaction to occur under mild conditions with a broad substrate scope and good functional group tolerance. Moreover, other C-based electrophiles, including alkenyl, alkynyl and alkyl halides, or pseudohalides, were also competent substrates for this reaction.

Rh(III)-Catalyzed Oxidative Domino C-H/N-H Annulation: Diarylureas as Arylamine Donors for the Assembly of Indolo[2,1-a]isoquinolines

An efficient and convenient Rh(III)-catalyzed double aryl C(sp2)-H bond and N-H activation and annulation reaction is reported for the synthesis of indolo[2,1-a]isoquinolines in the presence of the Cu(OAc)₂ oxidant under heating conditions. Distinct from previous works with other arylamine donors, one molecule of 1,3-diarylurea can serve as a precursor of two molecules of arylamine in the reaction with diaryl-substituted alkynes.

Picolinamides and Iodoalkynes Enable Palladium-Catalyzed syn-Aminoalkynylation of Di- and Trisubstituted Alkenes to Give Pyrrolidines

Palladium-catalyzed aminoalkynylation of electronically unbiased olefins with iodoalkynes is reported. The picolinamide auxiliary enables for the first time the syn-selective aminoalkynylation of mono-, di- and trisubstituted alkenes to afford the corresponding pyrrolidines in up to 97 % yield and as single diastereomers. Furthermore, through a C-H activation approach, the picolinamide allows the rapid synthesis of functionalized olefins, which are suitable cyclization precursors. Facile and orthogonal deprotection of the amides and Siⁱ Pr₃ -acetylenes in the products, and a subsequent Pictet-Spengler reaction is demonstrated.

Enantioselective Reductive N-Cyclization-Alkylation Reaction of Alkene-Tethered Oxime Esters and Alkyl Iodides by Nickel Catalysis

Asymmetric cross-electrophile difunctionalization of tethered alkenes has become a powerful tool for the production of chiral cyclic scaffolds; however, the current studies all focus on carbocyclization reactions. Herein, we report an N-cyclization-alkylation reaction and thus showcase the potential of heterocyclization for accessing new enantioenriched cyclic architectures. This work establishes a new approach for enantioselective aza-Heck cyclization/cross-coupling sequence, which remains a long-standing unsolved challenge for the synthetic community. The reaction proceeds with primary, secondary, and a few tertiary alkyl iodides, and the use of newly defined ligands gave highly enantioenriched pyrrolines with improved molecular diversity under mild conditions. The presence of imine functionality allows for further structural variations.