Regiocontrolled Cobalt-Catalyzed Diels−Alder Reactions of Silicon-Functionalized, Terminal, and Internal Alkynes

Cobalt-Catalyzed Divergent Cycloadditions of Alkynes with Conjugated Dienes Yielding 3-Vinylcyclobutenes, Bicyclo[3.1.0]hexenes, and Cyclohexa-1,4-dienes

A traditional cobalt catalyst system still contains undiscovered reactivity. Depending on the tertiary phosphines and substrates used, the catalytic system using CoBr₂/tertiary phosphine/Zn/ZnI₂ catalyzes divergent cycloadditions of internal alkynes with conjugated dienes, yielding 3-alkenylcyclobut-1-enes, bicyclo[3.1.0]hexenes, and cyclohexa-1,4-dienes. A [CoBr₂(PPh₃)₂]/Zn/ZnI₂-catalyzed reaction of 3-hexyne (1a) with 1-(4-methoxyphenyl)butadiene (2a) at room temperature in CH₂Cl₂ exclusively produces a [2 + 2] cycloaddition product (E)-2-(2,3-diethylcyclobut-2-ene-1-yl)vinyl-4-methoxybenzene (3aa). When [CoBr₂(dppp)]/Zn/ZnI₂ is used as a catalyst, a bicyclic compound 6-(4-methoxyphenyl)-2,3-diethylbicyclo[3.1.0]hex-2-ene (4aa) is dominantly formed in a 77% yield. The CoBr₂/dppe/Zn/ZnI₂ system can undergo a [2 + 4] cycloaddition to yield 3-(4-anisyl)-1,2-diethylcyclohexa-1,4-diene (5aa) as the dominant product in 38% yield. The bite angles of the ligands used contribute significantly to this catalytic diversity.

Photochemical alknylation of hydrosilanes by iron catalysis

Alkynylsilanes is one kind of essential synthetic block in organic chemistry. The established synthetic routes remain some drawbacks regarding to harsh reaction conditions or expensive/rare metal catalyst. Herein, we report...

Alkynes as Privileged Synthons in Selected Organic Name Reactions

BACKGROUND

Alkynes are actually basic chemicals, serving as privileged synthons for planning new organic reactions for assemblage of a reactive motif, which easily undergoes a further desirable transformation. Name reactions, in organic chemistry are referred to those reactions which are well-recognized and reached to such status for being called as their explorers, discoverers or developers. Alkynes have been used in various name reactions. In this review, we try to underscore the applications of alkynes as privileged synthons in prevalent name reactions such as Huisgen 1,3-dipolar cycloaddtion via Click reaction, Sonogashira reaction, and Hetero Diels-Alder reaction.

OBJECTIVE

In this review, we try to underscore the applications of alkynes as privileged synthons in the formation of heterocycles, focused on the selected reactions of alkynes as a synthon or impending utilization in synthetic organic chemistry, which have reached such high status for being included in the list of name reactions in organic chemistry.

CONCLUSION

Alkynes (including acetylene) are an unsaturated hydrocarbon bearing one or more triple C-C bond. Remarkably, alkynes and their derivatives are frequently being used as molecular scaffolds for planning new organic reactions and installing reactive functional group for further reaction. It is worth mentioning that in general, the terminal alkynes are more useful and more frequently being used in the art of organic synthesis. Remarkably, alkynes have found different applications in pharmacology, nanotechnology, as well as being known as appropriate starting precursors for the total synthesis of natural products and biologically active complex compounds. They are predominantly applied in various name reactions such as Sonogashira, Glaser reaction, Friedel-crafts reaction, Castro-Stephens coupling, Huisgen 1.3-dipolar cycloaddtion reaction via Click reaction, Sonogashira reaction, hetero-Diels-Alder reaction. In this review, we tried to impress the readers by presenting selected name reactions, which use the alkynes as either stating materials or precursors. We disclosed the applications of alkynes as a privileged synthons in several popular reactions, which reached to such high status being classified as name reactions. They are thriving and well known and established name reactions in organic chemistry such as Regioselective, 1,3-dipolar Huisgen cycloaddtion reaction via Click reaction, Sonogashira reaction and Diels-Alder reaction.

Pyridine(diimine) Iron Diene Complexes Relevant to Catalytic [2+2]-Cycloaddition Reactions

The synthesis, characterization, and catalytic activity of pyridine(diimine) iron piperylene and isoprene complexes are described. These diene complexes are competent precatalysts for (i) the selective cross-[2+2]-cycloaddition of butadiene or (E)-piperylene with ethylene and α-olefins and (ii) the 1,4-hydrovinylation of isoprene with ethylene. In the former case, kinetic analysis implicates the diamagnetic η4-piperylene complex as the resting state prior to rate-determining oxidative cyclization. Variable temperature 1H NMR and EXSY experiments established that diene exchange from the diamagnetic, 18e- complexes occurs rapidly in solution at ambient temperature through a dissociative mechanism. The solid-state structure of (Me(Et)PDI)Fe(η4-piperylene) (Me(Et)PDI = 2,6-(2,6-Me2-C6H3N═CEt)2C5H3N), was determined by single-crystal X-ray diffraction and confirmed the s-trans coordination of the monosubstituted 1,3-diene. Possible relationships between ligand-controlled diene coordination geometry, metallacycle denticity, and chemoselectivity of iron-mediated cycloaddition reactions are discussed.

Metal-catalyzed regiodivergent organic reactions

This review discusses metal-catalysed regiodivergent additions, allylic substitutions, CH-activation, cross-couplings and intra- or intermolecular cyclisations.

Cobalt-catalyzed regioselective syntheses of indeno[2,1-c]pyridines from nitriles and diynes bearing propargyl fragments

A highly efficient CoI2/o-phenanthroline catalyzed cycloaddition reaction of diynes bearing TBS protected propargylic alcohol fragments with nitriles has been developed. This methodology offers regioselective access, with good functional group tolerance, to various indeno[2,1-c]pyridine derivatives in moderate to excellent yields. It was found that o-phenanthroline as a bidentate nitrogen ligand showed high efficacy in this cycloaddition reaction.

Diversity-Oriented Approaches to Polycyclics and Bioinspired Molecules via the Diels-Alder Strategy: Green Chemistry, Synthetic Economy, and Beyond

We describe diverse approaches to various dienes and their utilization in the Diels-Alder reaction to produce a variety of polycycles. The dienes covered here are prepared by simple alkylation reaction or via the Claisen rearrangement or by enyne metathesis of alkyne or enyne building blocks. Here, we have also included the Diels-Alder chemistry of dendralenes, a higher analog of cross-conjugated dienes. The present article is inclusive of o-xylylene derivatives that are generated in situ starting with benzosultine or benzosulfone derivatives. The Diels-Alder reaction of these dienes with various dienophiles gave diverse polycyclic systems and biologically important targets.

Understanding the regioselectivity in Scholl reactions for the synthesis of oligoarenes

A short reaction sequence leads to oligoarene derivatives utilising a regioselective Scholl reaction for the unprecedented cyclisation to the mono-functionalised oligoarene under methanol elimination. Quantum-chemical investigations reveal the reason for the remarkably high regioselectivity.

Cobalt catalysis at the crossroads: cobalt-catalyzed Alder-ene reaction versus [2 + 2] cycloaddition

The application of bidentate phosphine ligands in cobalt-catalyzed transformations of cyclic alkenes such as cyclopentene and cycloheptene with internal alkynes led to a chemoselective Alder-ene or a [2 + 2] cycloaddition reaction depending on the electronic nature of the alkyne and the bite angle of the ligand used.