The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Paolo Quadrelli - One of the best experts on this subject based on the ideXlab platform.
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cycloadditions of nitrile oxides to α β unsaturated aldehydes frontier orbital interactions and secondary orbital interactions at work in determining Regiochemistry
Tetrahedron, 2000Co-Authors: Lucio Toma, G Perrini, Antonino Corsaro, Paolo Quadrelli, Cristiana Di Valentin, Ricardo Gandolfi, Pierluigi CaramellaAbstract:Abstract The Regiochemistry of the cycloadditions of nitrile oxides to crotonaldehyde and cinnamaldehyde has been determined and is dictated by frontier orbital interactions and secondary orbital interactions as well. In cycloadditions to α,β-unsaturated compounds the directive effect of the frontier orbital interactions can be diverted by steric drifts and secondary orbital interactions.
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cycloaddition of nitrile oxides to cyclic and acyclic α β unsaturated amides frontier orbital interactions and an unexpected steric drift determine Regiochemistry
Tetrahedron, 1999Co-Authors: Pierluigi Caramella, Daniela Reami, Mario Falzoni, Paolo QuadrelliAbstract:Abstract The Regiochemistry of the cycloadditions of nitrile oxides to α,β-unsaturated amides is determined by frontier orbital interactions and by a regiochemical drift due to steric effects. Cycloadditions to α,β-unsaturated lactames afford mainly 4-carboxamido-isoxazolines with high regioselectivity. In cycloadditions to acyclic α,β-unsaturated amides the regioselectivity relaxes and finally reverses in the case of N,N-disubstituted derivatives, because of the increasing steric congestion at the amine nitrogen.
Hiroyuki Ishibashi - One of the best experts on this subject based on the ideXlab platform.
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controlling the Regiochemistry of radical cyclizations
ChemInform, 2006Co-Authors: Hiroyuki IshibashiAbstract:This review describes the results of our recent studies on the control of the Regiochemistry of radical cyclizations. N-vinylic α-chloroacetamides generally cyclized in a 5-endo-trig manner to give five-membered lactams, whereas 4-exo-trig cyclization occurred when the cyclized radical intermediates were highly stabilized by an adjacent phenyl or phenylthio group to afford β-lactams. The 5-exo or 6-exo cyclization of aryl radicals onto the alkenic bond of enamides could be shifted to the corresponding 6-endo or 7-endo mode of cyclization by a positional change of the carbonyl group of enamides. The 6-endo- and 7-endo-selective aryl radical cyclizations were applied to radical cascades for the synthesis of alkaloids such as phenanthroindolizidine, cephalotaxine skeleton, and lennoxamine. The 5-exo-trig cyclization of an alkyl radical onto the alkenyl bond of enamides could also be shifted to the 6-endo mode by a positional change of the carbonyl group of enamides. The 6-endo- selective cyclization was applied to the radical cascade to afford a cylindricine skeleton. Other examples of controlling the Regiochemistry of radical cyclizations and their applications to the synthesis of natural products are also discussed. © 2006 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 6: 23–31; 2006: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20069
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Regiochemistry in aryl radical cyclization onto methylenecycloalkanes
Journal of Organic Chemistry, 2000Co-Authors: Hiroyuki Ishibashi, Tetsuya Kobayashi, Sayaka Nakashima, Osamu TamuraAbstract:Bu(3)SnH-mediated aryl radical cyclization onto methylenecycloalkanes having a phenylthio, an ester, or a nitrile group at the terminus of the alkenic bond provides exclusively exo cyclization products. The results are in sharp contrast to those reported for nonsubstituted methylenecycloalkanes, which give exclusively endo cyclization products. Formation of endo cyclization products has been suggested to be a result of a consecutive 5-exo cyclization of an aryl radical and neophyl rearrangement. The exo-selective aryl radical cyclization offers a new method for synthesizing fused aromatic compounds containing a benzylic quaternary carbon atom.
Pierluigi Caramella - One of the best experts on this subject based on the ideXlab platform.
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cycloadditions of nitrile oxides to α β unsaturated aldehydes frontier orbital interactions and secondary orbital interactions at work in determining Regiochemistry
Tetrahedron, 2000Co-Authors: Lucio Toma, G Perrini, Antonino Corsaro, Paolo Quadrelli, Cristiana Di Valentin, Ricardo Gandolfi, Pierluigi CaramellaAbstract:Abstract The Regiochemistry of the cycloadditions of nitrile oxides to crotonaldehyde and cinnamaldehyde has been determined and is dictated by frontier orbital interactions and secondary orbital interactions as well. In cycloadditions to α,β-unsaturated compounds the directive effect of the frontier orbital interactions can be diverted by steric drifts and secondary orbital interactions.
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cycloaddition of nitrile oxides to cyclic and acyclic α β unsaturated amides frontier orbital interactions and an unexpected steric drift determine Regiochemistry
Tetrahedron, 1999Co-Authors: Pierluigi Caramella, Daniela Reami, Mario Falzoni, Paolo QuadrelliAbstract:Abstract The Regiochemistry of the cycloadditions of nitrile oxides to α,β-unsaturated amides is determined by frontier orbital interactions and by a regiochemical drift due to steric effects. Cycloadditions to α,β-unsaturated lactames afford mainly 4-carboxamido-isoxazolines with high regioselectivity. In cycloadditions to acyclic α,β-unsaturated amides the regioselectivity relaxes and finally reverses in the case of N,N-disubstituted derivatives, because of the increasing steric congestion at the amine nitrogen.
Osamu Tamura - One of the best experts on this subject based on the ideXlab platform.
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Regiochemistry in aryl radical cyclization onto methylenecycloalkanes
Journal of Organic Chemistry, 2000Co-Authors: Hiroyuki Ishibashi, Tetsuya Kobayashi, Sayaka Nakashima, Osamu TamuraAbstract:Bu(3)SnH-mediated aryl radical cyclization onto methylenecycloalkanes having a phenylthio, an ester, or a nitrile group at the terminus of the alkenic bond provides exclusively exo cyclization products. The results are in sharp contrast to those reported for nonsubstituted methylenecycloalkanes, which give exclusively endo cyclization products. Formation of endo cyclization products has been suggested to be a result of a consecutive 5-exo cyclization of an aryl radical and neophyl rearrangement. The exo-selective aryl radical cyclization offers a new method for synthesizing fused aromatic compounds containing a benzylic quaternary carbon atom.
Laren M Tolbert - One of the best experts on this subject based on the ideXlab platform.
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one electron oxidation of 9 methylanthracene and 9 trimethylsilyl methyl anthracene reversal of radical cation selectivity by the trimethylsilyl group
Journal of the American Chemical Society, 1991Co-Authors: Sarath R Sirimanne, Donald R Vanderveer, Laren M TolbertAbstract:Oxidation of 9-methylanthracene by pyridine/iodine proceeds mainly through nucleophilic attack on the intermediate anthracene radical cation rather than deprotonation. Replacement of a methyl proton by trimethylsilyl completely reverses the Regiochemistry
