Radical Cyclizations by Intramolecular Additions

Surzur, Jean‐Marie

doi:10.1007/978-1-4613-3192-6_3

Cited by 46 publications

(16 citation statements)

References 628 publications

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“…[3]) for which kSooC = 3.7 X lo8 s-' (18), and are comparable to the rates of 5-eso and 6-endo cyclizations of radical 15, eq. [4].…”

Section: H2nnhrmentioning

confidence: 56%

Facile 5-endo ring closures to the azo group. A free radical synthesis of indazoles

Kunka¹,

Warkentin²

1990

Can. J. Chem.

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Five 1-alkyl-3-methylindazoles were prepared by treatment of l-(2-bromophenyl)-l-methoxy-l-(2-alkylazo)ethanes with tri-n-butyl stannane and AIBN at 80°C in benzene. Yields in the radical cyclization step ranged from 39 to 92%. 1-Phenyl-3-methylindazole was prepared by an analogous route but in very poor yield (<5%). Rate constants for the 5-endo radical closures ( k: O: : ) , estimated by the radical clock method, were 5.2 X 10's-' and 9.2 X 10's-' for two of the alkyl systems. Rate constants for analogous 5-endo cyclizations of aryl radicals onto C-C double bonds are much smaller than those for cyclizations to the azo functional group.

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“…[3]) for which kSooC = 3.7 X lo8 s-' (18), and are comparable to the rates of 5-eso and 6-endo cyclizations of radical 15, eq. [4].…”

Section: H2nnhrmentioning

confidence: 56%

Facile 5-endo ring closures to the azo group. A free radical synthesis of indazoles

Kunka¹,

Warkentin²

1990

Can. J. Chem.

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“…or C−N . , the orthogonal overlap of the thiyl‐radical with the double or triple bond allows for cyclization to occur readily at either position of the alkene or alkyne . It has been observed that in the case of terminal alkenes and alkynes, the thiyl‐radical will react predominantly with the terminus of the unsaturation.…”

Section: Thiyl‐radical Cyclizationsmentioning

confidence: 99%

“…[40] The analogous cyclization reactions of alkoxyl-and aminylradicals are closely matched to those of carbon centered radicals but due to the greater bond length of the CÀ S * bond compared to CÀ C * , CÀ O * or CÀ N * , the orthogonal overlap of the thiyl-radical with the double or triple bond allows for cyclization to occur readily at either position of the alkene or alkyne. [7,41] It has been observed that in the case of terminal alkenes and alkynes, the thiyl-radical will react predominantly with the terminus of the unsaturation. This has been partly rationalized by back-bonding interactions of the unoccupied 3d orbitals on the S-atom with filled πorbital of the alkene or alkyne, thus reducing the geometric constraints of the cyclization transition state (TS).…”

Section: Thiyl-radical Cyclizationsmentioning

confidence: 99%

5‐exo versus 6‐endo Thiyl‐Radical Cyclizations in Organic Synthesis

McCourt

Scanlan

2019

Helvetica Chimica Acta

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Since the discovery of the radical mediated thiol‐ene and thiol‐yne reactions, these reactions have been employed in an intramolecular manner for the synthesis of sulfur‐containing heterocycles. Although closely related on a mechanistic basis, the thiol‐ene and thiol‐yne cyclization can differ greatly in regioselectivity and product distribution, with the thiol‐ene process being more predictable and thus attracting greater utilization. Herein, we review intramolecular thiyl‐radical addition reactions and the factors leading to the observed regioselectivity in examples in which both the 5‐exo and 6‐endo mode of cyclization are feasible. We highlight the applications of these important reactions for organic synthesis in the recent literature.

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“…With the addition of Br 2 finished, the reaction mixture was stirred for 4 h and allowed slowly to reach room temperature. The reaction mixture was then washed with aqueous Na 2 To induce oxidation of residual benzaldehyde and to make the purification easier, the crude product was exposed to air and daylight for about 24 h. Two chromatographic columns were necessary to obtain a pure product. A column of silica gel (petroleum ether/EtOAc 97:3) followed by a separation on silica gel impregnated with AgNO 3 (petroleum ether/EtOAc 98:2) afforded 5 as a colourless oil (0.09 g, 61 %, Z/E 91:9 1 H NMR (300 MHz, CDCl 3 ): δ = 2.43 (q, J = 7.6 Hz, 2 H), 2.86 (t, J = 7.6 Hz, 2 H), 6.13 (t, J = 7.6 Hz, 1 H), 7.00-7.36 (m, 13 H), 7.49 (dd, J = 7.9, 1.1 Hz, 1 H) ppm.…”

Section: -Bromo-2-(3-bromopropyl)benzene (9a)mentioning

confidence: 99%

“…[1][2][3][4] As proposed in a preceding work, radical clocks are radical probes for which reactive intramolecular rearrangements have been kinetically measured. [5] "Rearrangement" covers a variety of chemical acts occurring at the radical stage: racemisation, β-scission, hydrogen atom transfer, or addition to an unsat-specific second role.…”

Section: Introductionmentioning

confidence: 99%

Structural Effects in Radical Clocks and Mechanisms of Grignard Reagent Formation: Special Effect of a Phenyl Substituent in a Radical Clock when the Crossroads of Selectivity is at a Metal/Solution Interface

et al. 2009

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A large class of radical clocks is based on the intramolecular trapping of a reactive radical by a suitably located unsaturated system. Depending on the substituents present on this unsaturated system, the rate of cyclisation may vary drastically. This property has been repeatedly used to diagnose the participation of very short-lived radicals in the mechanisms of a wide variety of reactions. For reactions occurring in homogeneous solution, a phenyl substituent capable of stabilizing the radical formed during the act of trapping has been one of the most widely used tools of this type. During study of the mechanisms of formation of Grignard reagents -reactions that occur at the interface of the metal and the solution -the phenyl substituent displayed a specific new behaviour pattern. Besides its stabilizing role, it was also able to play the role of mediator in redox catalysis of electron transfer. In this case, the first events on the pathway to the Grignard reagents involve a cascade of three (one intermolecular followed by two intramolecular) electron transfers. Introduction of a p-methoxy substituent on the phenyl ring, making the phenyl group a poorer electron acceptor, suppresses this

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Radical Cyclizations by Intramolecular Additions

Cited by 46 publications

References 628 publications

Facile 5-endo ring closures to the azo group. A free radical synthesis of indazoles

Facile 5-endo ring closures to the azo group. A free radical synthesis of indazoles

5‐exo versus 6‐endo Thiyl‐Radical Cyclizations in Organic Synthesis

Structural Effects in Radical Clocks and Mechanisms of Grignard Reagent Formation: Special Effect of a Phenyl Substituent in a Radical Clock when the Crossroads of Selectivity is at a Metal/Solution Interface

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