N,S-Dimethyldithiocarbamyl oxalates as precursors for determining kinetic parameters for oxyacyl radicals

N,S-Dimethyldithiocarbamyl oxalates (e.g.6, 10) are novel, readily prepared precursors to alkyloxyacyl radicals 1 that are more suitable for kinetic studies than existing precursors; 10 has allowed the determination of accurate rate data for the cyclization of the butenyloxyacyl radical 5 (kc = 1.2 X 107 s-1 at 21 °C).</p

Use of monosaccharides in metal-catalyzed coupling reactions

The addition of monosaccharides to metal-catalyzed coupling reactions can be beneficial in terms of decreasing the time required, chemical waste products and overall cost of the process. Monosaccharides are used in a number of different ways, including (a) acting as a ligand for the metal, (b) providing the appropriate reduction potential for a chemical process and (c) acting as a reducing agent for the formation and stabilization of catalytically active metal nanoparticles. Recently, there has been a significant amount of research in this growing field and there is thus the potential for the addition of monosaccharides to coupling reactions to have a significant impact on the synthesis of the important small molecules on which we have all come to rely. This Perspectives Article will cover recent developments in the addition of monosaccharides to metal-catalyzed coupling reactions with an emphasis on their utility and limitations in order to facilitate the further development of this exciting area of research.</p

N,S-Dimethyldithiocarbamyl oxalates as precursors for determining kinetic parameters for oxyacyl radicals

N,S-Dimethyldithiocarbamyl oxalates (e.g.6, 10) are novel, readily prepared precursors to alkyloxyacyl radicals 1 that are more suitable for kinetic studies than existing precursors; 10 has allowed the determination of accurate rate data for the cyclization of the butenyloxyacyl radical 5 (kc = 1.2 X 107 s-1 at 21 °C).</p

Intramolecular homolytic substitutions in synthesis

Free radical chemistry contributes to the modern chemists’ toolbox in ways that were unimaginable only a few decades ago. There can be no doubt that the construction of carbocyclic and heterocyclic ring systems through the intramolecular addition of alkyl, aryl, and other radicals to unsaturated functionalities is a major contribution to synthetic methodology; this chemistry is the topic of other contributions to this collective work.</p

Ab initio studies of carbonyl radical additions to hydrazone systems

Ab initio and DFT calculations reveal that intermolecular radical additions of both acyl and oxyacyl radials to hydrazones occur through SOMO-pi*hydrazone, pihydrazone-SOMO and LPN-SOMO interactions between the radical and the hydrazone pi-system. Both acetyl and methoxycarbonyl radicals show preference for addition to the carbon end of the carbon-nitrogen pi-bond. At the highest level of theory used in this study (G2//MP2(full)/6-31G*), energy barriers of 11.2 and 22.6 kJ mol1 are calculated for acetyl radical addition to the carbon and nitrogen-ends of N-aminomethanimine respectively. The analogous energy barriers for the methoxycarbonyl radical are 4.9 and 25.7 kJ mol -1 at the same level of theory.</p

Ab initio studies of carbonyl radical additions to hydrazone systems

Ab initio and DFT calculations reveal that intermolecular radical additions of both acyl and oxyacyl radials to hydrazones occur through SOMO-pi*hydrazone, pihydrazone-SOMO and LPN-SOMO interactions between the radical and the hydrazone pi-system. Both acetyl and methoxycarbonyl radicals show preference for addition to the carbon end of the carbon-nitrogen pi-bond. At the highest level of theory used in this study (G2//MP2(full)/6-31G*), energy barriers of 11.2 and 22.6 kJ mol1 are calculated for acetyl radical addition to the carbon and nitrogen-ends of N-aminomethanimine respectively. The analogous energy barriers for the methoxycarbonyl radical are 4.9 and 25.7 kJ mol -1 at the same level of theory.</p

Use of monosaccharides in metal-catalyzed coupling reactions

The addition of monosaccharides to metal-catalyzed coupling reactions can be beneficial in terms of decreasing the time required, chemical waste products and overall cost of the process. Monosaccharides are used in a number of different ways, including (a) acting as a ligand for the metal, (b) providing the appropriate reduction potential for a chemical process and (c) acting as a reducing agent for the formation and stabilization of catalytically active metal nanoparticles. Recently, there has been a significant amount of research in this growing field and there is thus the potential for the addition of monosaccharides to coupling reactions to have a significant impact on the synthesis of the important small molecules on which we have all come to rely. This Perspectives Article will cover recent developments in the addition of monosaccharides to metal-catalyzed coupling reactions with an emphasis on their utility and limitations in order to facilitate the further development of this exciting area of research.</p

Intramolecular homolytic substitutions in synthesis

Free radical chemistry contributes to the modern chemists’ toolbox in ways that were unimaginable only a few decades ago. There can be no doubt that the construction of carbocyclic and heterocyclic ring systems through the intramolecular addition of alkyl, aryl, and other radicals to unsaturated functionalities is a major contribution to synthetic methodology; this chemistry is the topic of other contributions to this collective work.</p

An ab initio and DFT study of radical addition reactions of imidoyl and thioyl radicals to methanimine

Ab initio and DFT calculations reveal that both imidoyl and thioyl radicals add to the nitrogen end of methanimine through simultaneous SOMO-pi*imine, SOMO-piimine, SOMO-LPN and pi*radical-LPN interactions between the radical and the imine. At the CCSD(T)/cc-pVDZ//BHandHLYP/cc-pVTZ level of theory, barriers of 13.8 and 26.1 kJ mol-1 are calculated for the attack of the methylimidoyl radical at the carbon- and nitrogen- end of methanimine, respectively, indicating that the imidoyl radial has a preference for addition to the nitrogen end of imine. On the other hand, barriers of 25.1 and 13.4 kJ mol-1 are calculated at the same level of theory for the addition reaction of the methanethioyl radical at the carbon- and nitrogen- end of methanimine, respectively. Natural bond orbital (NBO) analysis at the BHandHLYP/6-311G** level of theory reveals that SOMO-pi*imine, SOMO-piimine, SOMO-LPN and pi*radical-LPN interactions are worth 111, 89, 115 and 17 kJ mol-1, respectively, in the transition state (4) for the reaction of methylimidoyl radical at the nitrogen end of methanimine; similar interactions are observed for the chemistry involving all the radicals studied here. These multi-component interactions are responsible for the unusual motion vectors associated with the transition states involved in these reactions.</p

Multi-component orbital interactions during oxyacyl radical addition reactions involving imines and electron-rich olefins

Ab initio and DFT calculations reveal that oxyacyl radicals add to imines and electron-rich olefins through simultaneous SOMO-pi*, SOMO-pi and pi*-HOMO interactions between the radical and the radicalophile. At the BHandHLYP/aug-cc-pVDZ level, energy barriers of 20.3 and 22.0 kJ mol -1 are calculated for the attack of methoxycarbonyl radical at the carbon and nitrogen ends of methanimine, respectively. In comparison, barriers of 22.0 and 8.6 kJ mol-1 are calculated at BHandHLYP/aug-cc-pVDZ for reaction of methoxycarbonyl radical at the 1- and 2-positions in aminoethylene, respectively. Natural bond orbital (NBO) analysis at the BHandHLYP/6- 311G** level of theory reveals that SOMO-pi*, SOMO-pi and pi*-LP interactions are worth 111, 394 and 55 kJ mol-1 respectively in the transition state (8) for reaction of oxyacyl radical at the nitrogen end of methanimine; similar interactions are observed for the chemistry involving aminoethylene. These multi-component interactions are responsible for the unusual motion vectors associated with the transition states involved in these reactions.</p