Cobalt Catalysts for [2+2+2] Cycloaddition Reactions: Isolated Precatalysts and in situ Generated Catalysts

AbstractHomogeneous earth-abundant metal catalysis based on well-defined molecular complexes has achieved great advance in synthetic methodologies. However, sophisticated ligand, hazardous activator and multistep synthesis starting from base metal salts are generally required for the generation of active molecular catalysts, which may hinder their broad application in large scale organic synthesis. Therefore, the development of metal cluster catalysts formed in situ from simple earth-abundant metal salts is of importance for the practical utilization of base metal resource, yet it is still in its infancy. Herein, a mixture of catalytic amounts of cobalt (II) iodide and potassium tert-butoxide is discovered to be highly active for selective hydroboration of vinylarenes and dihydroboration of nitriles, affording a good yield of diversified hydroboration products that without isolation can readily undergo further one pot transformations. It should be highlighted that the alkoxide-pinacolborane combination acts as an efficient activation strategy to activate cobalt (II) iodide for the generation of metastable heterotopic cobalt catalysts in situ, which is proposed to be catalytically active species.

Download Full-text

Symmetrical tetra-β″-sulfoleno-meso-aryl-porphyrins — synthesis, spectroscopy and structural characterization

Journal of Porphyrins and Phthalocyanines ◽

10.1142/s1088424613501204 ◽

2014 ◽

Vol 18 (01n02) ◽

pp. 115-122 ◽

Cited By ~ 8

Author(s):

Srinivas Banala ◽

Klaus Wurst ◽

Bernhard Kräutler

Keyword(s):

Metal Complexes ◽

Crystal Structures ◽

Structural Characterization ◽

Building Blocks ◽

Cycloaddition Reactions ◽

One Pot

We report here the preparation (in "one-pot") of a tetra-β″-sulfoleno-meso-aryl-porphyrin in about 80% yield by using an optimized modification of Lindsey's variant of the Adler–Longo approach. The Zn ( II )-, Cu ( II )- and Ni ( II )-complexes of the symmetrical porphyrin were prepared and characterized spectroscopically. Crystal structures of the fluorescent Zn ( II )- and of the non-fluorescent Ni ( II )-tetra-β″-sulfoleno-meso-aryl-porphyrinates showed the highly substituted porphyrin ligands to be nearly perfectly planar. The Zn ( II )-complex of this porphyrin has been used as a thermal precursor of a reactive diene, and — formally — of lateral and diagonal bis-dienes, of a tris-diene and of a tetra-diene, which all underwent [4 + 2]-cycloaddition reactions in situ with a range of dienophiles. Thus, the tetra-β″-sulfoleno-meso-aryl-porphyrin and its metal complexes represent reactive building blocks, "programmed" for the syntheses of symmetrical and highly functionalized porphyrins.

Download Full-text

Recent Advances of 1,3,5-Triazinanes in Aminomethylation and Cycloaddition Reactions

Synthesis ◽

10.1055/s-0040-1707160 ◽

2020 ◽

Vol 52 (17) ◽

pp. 2469-2482

Author(s):

Jia-Rong Chen ◽

Dong Liang ◽

Wen-Jing Xiao

Keyword(s):

Reaction Mechanisms ◽

Short Review ◽

Cycloaddition Reactions ◽

Recent Advances ◽

Nitrogen Containing Compounds

1,3,5-Trisubstituted 1,3,5-triazinanes (hexahydro-1,3,5-triazines), as stable and readily available surrogates for formaldimines, have found extensive applications for the construction of various nitrogen-containing compounds. The formaldimines, formed in situ from this reagent class, can participate in various aminomethylation and cycloaddition reactions. This short review presents recent advances in this field with emphasis on the conceptual ideas behind the developed methodologies and the reaction mechanisms.1 Introduction2 Aminomethylations with 1,3,5-Triazinanes3 Cycloadditions with 1,3,5-Triazinanes3.1 Use of 1,3,5-Triazinanes as Two-Atom Synthons3.2 Use of 1,3,5-Triazinanes as Three-Atom Synthons3.3 Use of 1,3,5-Triazinanes as Four-Atom Synthons3.4 Use of 1,3,5-Triazinanes as Six-Atom Synthons4 Conclusions

Download Full-text

Synthesis of Oxazoline and Oxazole Derivatives by Hypervalent-Iodine-Mediated Oxidative Cycloaddition Reactions

Synthesis ◽

10.1055/s-0040-1707122 ◽

2020 ◽

Vol 52 (16) ◽

pp. 2299-2310 ◽

Cited By ~ 4

Author(s):

Akira Yoshimura ◽

Akio Saito ◽

Viktor V. Zhdankin ◽

Mekhman S. Yusubov

Keyword(s):

Heterocyclic Compounds ◽

Short Review ◽

Active Species ◽

Hypervalent Iodine ◽

Cycloaddition Reactions ◽

Iodine Species ◽

Oxazole Derivatives

Organohypervalent iodine reagents are widely used for the preparation of various oxazolines, oxazoles, isoxazolines, and isoxazoles. In the formation of these heterocyclic compounds, hypervalent iodine species can serve as the activating reagents for various substrates, as well as the heteroatom donor reagents. In recent research, both chemical and electrochemical approaches toward generation of hypervalent iodine species have been utilized. The in situ generated active species can react with appropriate substrates to give the corresponding heterocyclic products. In this short review, we summarize the hypervalent-iodine-mediated preparation of oxazolines, oxazoles, isoxazolines, and isoxazoles starting from various substrates.1 Introduction2 Synthesis of Oxazolines3 Synthesis of Oxazoles4 Synthesis of Isoxazolines5 Synthesis of Isoxazoles6 Conclusion

Download Full-text

[4 + 2]-Cycloaddition Reactions Involving α-Oxo Thioketone Intermediates

Zeitschrift für Naturforschung B ◽

10.1515/znb-2002-0813 ◽

2002 ◽

Vol 57 (8) ◽

pp. 922-927 ◽

Cited By ~ 7

Author(s):

Mohamed I. Hegab ◽

Abd El-Galil A. Amr ◽

Farouk M. E. Abdel-Megeid

Keyword(s):

Cycloaddition Reactions ◽

Iodide Ions ◽

Sulfenyl Chlorides ◽

Chalcone Derivative

α-Chloro β-oxo sulfenyl chlorides 2 were reduced by iodide ions to the corresponding α-oxo thioketones 3 which dimerized in situ in a hetero-[4 + 2] cycloaddition to give the 1,3,4- oxadithiin derivatives 4. The α-oxo thioketones 3, in situ, cyclized also with 2,3-dimethyl-1,3- butadiene to give the corresponding adducts 5 and only in case of the oxo thioketone intermediate 3d two products 4d and 5d were obtained. Also, The α-oxo thioketones 3a,c, underwent in situ, cycloaddition with furan to give the corresponding adducts 6a,c together with the corresponding thioketone dimers 4a,c. When this reaction was carried out in the presence of diethyl acetylenedicarboxylate or chalcone derivative 8, only the oxo thioketone dimers 4a-d were obtained.

Download Full-text