3 Ruthenium-Catalyzed Azide–Alkyne Cycloaddition (RuAAC)

Under ruthenium catalysis, 1,5-disubstituted 1,2,3-triazoles can be accessed with high selectivity from terminal alkynes and organic azides via a ruthenium-catalyzed azide–alkyne cycloaddition (RuAAC) reaction. These conditions also allow the use of internal alkynes, providing access to 1,4,5-trisubstituted 1,2,3-triazoles. This chapter reviews the scope and limitations of the RuAAC reaction, as well as selected applications. A brief mention of azide–alkyne cycloaddition reactions catalyzed by other metals is also included.

Oxidative [4+2] Annulation of 1-Naphthols with Alkynes Accelerated by an Electron-Deficient Rhodium(III) Catalysts

The 1,3-diethoxycarbonyl-2,4,5-trimethylcyclopentadienyl (CpE) rhodium(III) complex displayed high efficacy in the catalytic oxidative annulation of 1-naphthols with internal alkynes under mild conditions. DFT calculations revealed that lower activation energies for the...

Catalytic and mechanistic studies of a highly active and E-selective Co(II) PNNH pincer catalyst system for transfer-semihydrogenation of internal alkynes

Herein we report the application of a Co(II) PNNH pincer catalyst system (PNNH = 2-(5-(t-butyl)-1H-pyrazol-3-yl)-6-(dialkylphosphinomethyl)pyridine) for the highly E-selective transfer semihydrogenation of internal diaryl alkynes using methanol and ammonia borane...

Palladium-Catalyzed Asymmetric Hydrophosphination of Internal Alkynes: Highly Regio- and Stereoselective Construction of Axially Chiral Phosphines

Palladium-catalyzed unprecedented atroposelective hydrophosphination of internal alkynes has been realized using diarylphosphines, affording C-N axially chiral trisubstituted olefins (vinylphosphines) in excellent regioselectiviry, (E)-selectivity, and enantioselectivity. The axial chirality was established via integration of hydrophosphination and dynamic kinetic transformation of the alkynes, with both symmetrical and nonsymmetrical secondary phosphines being applicable. In the latter case, additional P-central chirality has been constructed in good diastereoselectivity.

SOMOphilic Alkynylation of Unreactive Alkenes Enabled by Iron-Catalyzed Hydrogen Atom Transfer

We report an efficient and practical iron-catalyzed hydrogen atom transfer protocol for assembling acetylenic motifs into functional alkenes. Diversities of internal alkynes could be obtained from readily available alkenes and acetylenic sulfones with excellent Markovnikov selectivity. An iron hydride hydrogen atom transfer catalytic cycle was described to clarify the mechanism of this reaction.

Divergent Synthesis of Indolenine and Indoline Ring Systems by Palladium-Catalyzed Asymmetric Dearomatization of Indoles

Dearomatized indole derivatives bearing a C3- or C2-stereocenter exist ubiquitously in natural products and biologically active molecules. Despite remarkable advances in their chemical synthesis, stereoselective and regio-divergent methods are still in a high demand. Herein, a Pd-catalyzed intermolecular asymmetric spiroannulation of 2,3-disubstituted indoles with internal alkynes has been developed for the efficient construction of indoline structures with a C2-quaternary stereocenter. Stereospecific aza-semipinacol rearrangement of these indoline derivatives under acidic conditions afforded indolenine products bearing a C3-quaternary stereocenter, where the selectivity for the rearranging group could be controlled by the reaction sequence. The asymmetric spiroannulation together with the subsequent aza-semipinacol rearrangement enabled a divergent access to dearomatized indole derivatives with either a C3- or a C2-quaternary stereocenter.