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3. Regioselective Synthesis of 3‐Substituted Isocoumarin‐1‐imines via Palladium‐Catalyzed Denitrogenative Transannulation of 1,2,3‐Benzotriazin‐4(3H)‐ones and Terminal Alkynes.

Author

Balakrishnan, Madasamy Hari, Sureshbabu, Popuri, Korivi, Ramaraju, and Mannathan, Subramaniyan

Subjects
COUMARINS, ALKYNES, FUNCTIONAL groups, EXTRUSION process
Abstract

A palladium‐catalyzed denitrogenative transannulation strategy to access various 3‐substituted isocoumarin‐1‐imine frameworks using 1,2,3‐benzotriazin‐4(3H)‐ones and terminal alkynes is described. The reaction is highly regioselective and tolerates a wide range of functional groups. The reaction is believed to proceed via a five‐membered palladacycle intermediate extruding environmentally benign molecular nitrogen as a by‐product. The utility of this method was showcased through the one‐pot synthesis of biologically relevant 3‐substituted isocoumarin scaffolds. [ABSTRACT FROM AUTHOR]

Published
2023
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4. Sustainable Bioengineering of Gold Structured Wide-Area Supported Catalysts for Hand-Recyclable Ultra-Efficient Heterogeneous Catalysis

Author

Bhatt, Chandra S., primary, Parimi, Divya S., additional, Bollu, Tharun K., additional, H. U, Madhura, additional, Jacob, Noah, additional, Korivi, Ramaraju, additional, Ponugoti, Sai S., additional, Mannathan, Subramaniyan, additional, Ojha, Sunil, additional, Klingner, Nico, additional, Motapothula, M., additional, and Suresh, Anil K., additional

Published
2022
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12. Quaternary ammonium hydroxide‐functionalized g‐C3N4 catalyst for aerobic hydroxylation of arylboronic acids to phenols.

Author

Muhammad, Ibrahim, Mannathan, Subramaniyan, and Sasidharan, Manickam

Subjects
*CATALYSTS, *PHENOLS, *HYDROXYLATION, *ION exchange resins, *TRANSMISSION electron microscopes, *NITRIDES, *AMMONIUM hydroxide
Abstract

A new and efficient metal‐free approach toward the synthesis of phenols via an aerobic hydroxylation of arylboronic acids by using a novel quaternary ammonium hydroxide g‐C3N4 catalyst has been described. The functionalized quaternary ammonium hydroxide (g‐C3N4‐OH) has been prepared from graphitic carbon nitride (g‐C3N4) scaffold by converting the residual –NH2 and –NH groups to quaternary methyl ammonium iodide by performing a methylation reaction with methyl iodide followed by ion‐exchange with 0.1 N KOH or anion exchange resin Amberlyst A26 (OH‐ form) by post‐synthetic modification. The resultant g‐C3N4‐OH was characterized by XRD, FTIR, field‐emission scanning electron microscope (FESEM), high‐resolution transmission electron microscope (HRTEM), N2 adsorption/desorption isotherms, and acid–base titration. Tested as solid‐base catalysts, the g‐C3N4‐OH showed excellent catalytic activity in the aerobic hydroxylation reaction by converting a variety of arylboronic acids to the corresponding phenols in high yields. More importantly, the g‐C3N4‐OH solid‐base has been successfully reused four times with the minor loss of initial catalytic activity (10.5%). [ABSTRACT FROM AUTHOR]

Published
2020
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15. Quaternary ammonium hydroxide‐functionalized g‐C3N4catalyst for aerobic hydroxylation of arylboronic acids to phenols

Author

Muhammad, Ibrahim, Mannathan, Subramaniyan, and Sasidharan, Manickam

Abstract

A new and efficient metal‐free approach toward the synthesis of phenols via an aerobic hydroxylation of arylboronic acids by using a novel quaternary ammonium hydroxide g‐C3N4catalyst has been described. The functionalized quaternary ammonium hydroxide (g‐C3N4‐OH) has been prepared from graphitic carbon nitride (g‐C3N4) scaffold by converting the residual –NH2and –NH groups to quaternary methyl ammonium iodide by performing a methylation reaction with methyl iodide followed by ion‐exchange with 0.1 N KOH or anion exchange resin Amberlyst A26 (OH‐ form) by post‐synthetic modification. The resultant g‐C3N4‐OH was characterized by XRD, FTIR, field‐emission scanning electron microscope (FESEM), high‐resolution transmission electron microscope (HRTEM), N2adsorption/desorption isotherms, and acid–base titration. Tested as solid‐base catalysts, the g‐C3N4‐OH showed excellent catalytic activity in the aerobic hydroxylation reaction by converting a variety of arylboronic acids to the corresponding phenols in high yields. More importantly, the g‐C3N4‐OH solid‐base has been successfully reused four times with the minor loss of initial catalytic activity (10.5%). An efficient and simple metal‐free method of preparing novel quaternary ammonium hydroxide‐functionalized (g‐C3N4) catalysts has been described for the first time. The as‐synthesized quaternary ammonium hydroxide (g‐C3N4‐OH) catalyst efficiently promotes aerobic hydroxylation of arylboronic acids to phenols when used as a solid base. The solid base produced (g‐C3N4‐OH) has been reused for four successive recycles, which retains 90% of initial catalytic activity.

Published
2020
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23. Palladium/Copper-Catalyzed Denitrogenative Alkylidenation and ortho-Alkynylation Reaction of 1,2,3-Benzotriazin-4(3H)-ones

Author

Hari Balakrishnan, Madasamy and Mannathan, Subramaniyan

Abstract

An efficient palladium-catalyzed approach to access various functionalized (Z)-3-benzylidene-isoindoline-1-ones and (Z)-3-benzylidene(imino)isobenzofuranones via a denitrogenative tandem alkynylation/cyclization reaction of 1,2,3-benzotriazin-4(3H)-ones with aromatic terminal alkynes is described. Furthermore, a denitrogenative ortho-alkynylation reaction of 1,2,3-benzotriazinones with aliphatic terminal alkynes is also developed. The reaction proceeds through a five-membered azapalladacyclic intermediate with the extrusion of a nitrogen molecule. The significance of the reaction is also demonstrated by a one-pot synthesis of (Z)-3-benzylideneisobenzofuran-1(3H)-one derivatives in good to high yields.

Published
2020
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27. Importance of the Reducing Agent in Direct Reductive Heck Reactions.

Author

Raoufmoghaddam, Saeed, Mannathan, Subramaniyan, Minnaard, Adriaan J., de Vries, Johannes G., de Bruin, Bas, and Reek, Joost N. H.

Subjects
*CARBENES, *CARBON compounds, *CHEMOSELECTIVITY, *REACTIVITY (Chemistry), *DYNAMICS
Abstract

Abstract: The role of the reductant in the palladium N‐heterocyclic carbene (NHC) catalyzed reductive Heck reaction and its effect on the mechanism of the reaction is reported. For the first time in this type of transformation, the palladium‐NHC‐catalyzed reductive Heck reaction was shown to proceed in the presence of LiOMe and iPrOH even at 10 °C to give the products very efficiently in excellent yields and with exceptional chemoselectivities. This study shows that the reaction proceeds through two distinct mechanisms that depend on the nature of the reducing agent. In the presence of a protic solvent or acidic medium the reaction undergoes protonation to yield the reduced product, whereas in the absence of proton source, it proceeds through the insertion of the reductant followed by reductive elimination. The kinetic data reveal that the oxidative addition is the rate‐determining step in the reaction. The reaction profiles show first‐order kinetics in aryl iodide and Pd and zero‐order kinetics in LiOMe, benzylideneacetone, and the excess amount of NHC ligand. In addition, the reaction progress kinetic analysis shows that neither catalyst decomposition nor product inhibition occurs during the reaction. DFT calculations of the key steps confirm that the oxidative addition step is the rate‐determining step in the reaction. Deuterium‐labeling experiments indicate that the product is formed by the protonation of the Pd−Calkyl bond of the intermediate formed after enone insertion into the Pd−CAr bond. Application of chiral NHC ligands in the asymmetric reductive Heck reaction only results in poor enantioselectivities (enantiomeric excess up to 20 %) and is also substrate specific. DFT calculations suggest that the migration of the aryl group to the alkene of the substrate is the enantioselectivity‐determining step of the reaction. It is further shown that if the steric bulk at the enone is small (a methyl group), the two transition state barriers from [PdII(L2)(ArI)(enone)] species Cre and Csi, which have the re and si face of the enone substrate coordinated to Pd, are very similar, in line with the experimental results. With a slightly larger group (an isopropyl substituent) a significant difference in energy barriers is calculated (2.6 kcal mol−1), and in the experiment this product is formed with a modest enantiomeric excess (up to 20 %). [ABSTRACT FROM AUTHOR]

Published
2018
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