Nuclear polarization in a thermal 1,3-sigmatropic rearrangement. Evidence for a radical pathway

Baldwin, Jack E.; Brown, James Edward

doi:10.1021/ja01041a039

Cited by 26 publications

(2 citation statements)

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“…5 Hz, 4-H,), 7.36 (q, J 7.5 Hz, CH,CH,), and 8.87 (t, J 7. 5 Hz, CH,CH,). CinnamyZ 3, .-3,3-Dimethyl-ally1 bromide (20.0 g) in dry tetrahydrofuran (50 ml) was slowly added with stirring to a mixture of sodium hydride (3.0 g ) and cinnamyl alcohol (13.4 g ) in dry tetrahydrofuran (dt, J 16, 6.5 Hz, 5-H), 4.04 (d, J 15 Hz, 1-H), 4.18 (dd, (50 ml).…”

Section: -Methoxy-44-dimethye-l-phenyzhexa-l5-diene (25d) -mentioning

confidence: 96%

“…Bromide.-2-Benzoyl-9-bromofluorene (3.0 g) was stirred at room temperature overnight with NN-dimethylcinnamylamine (1.5 g) in dry methyl cyanide (50 ml). The resulting solution was added to dry ether (500 ml) and the precipitated gummy solid purified by repeated precipitation from chloroform by the addition of ether giving the salt as a pale brown gum (3.8 g, 90%) which was suitable for use in the following experiment, 7 2.02-2.78 (m, 17 aromatic H), 3.00 (d, J 15 Hz, CH=CH), 3.62 (dt, J 15, 8 Mz, CH=CH), 4.39 (s, 9-H), 5.79 (d, J 8 Hz, CH,CH=CH), and 6.80 ( s , NMe,) .…”

Section: Cinnamye-9-(2-benzoyljhorenyl)dimethylammoniummentioning

confidence: 99%

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Base catalysed rearrangements involving ylide intermediates. Part 4. [1,3] Sigmatropic rearrangements of 4-dimethylaminobutenes and [3,3] sigmatropic rearrangements of 3-dimethylaminohexa-1,5-dienes

Jemison¹,

Ollis²,

Sutherland³

et al. 1980

J. Chem. Soc., Perkin Trans. 1

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The [1,3] sigmatropic rearrangement (1 1) + (1 2) of the 9-dimethyIamino-9-(1 -phenylallyl)fluorene is a stereoselective process (84 : 16) at 170". Analogous [1,3] rearrangements (1 6) + (1 7) of other fluorene derivatives show that the reaction rate is increased by electron donating 9-substituents in the order 0-> NMe, > OMe. Similar substituent effects are observed for the [3,3] Cope rearrangement (25) + (26) of hexa-1,5-dienes. 4-Pheny1, 4,4-dimethyl, and 3-dimethylamino substituents are particularly effective in accelerating the rate of the rearrangement (25) --w (26).

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Section: -Methoxy-44-dimethye-l-phenyzhexa-l5-diene (25d) -mentioning

confidence: 96%

Section: Cinnamye-9-(2-benzoyljhorenyl)dimethylammoniummentioning

confidence: 99%

Base catalysed rearrangements involving ylide intermediates. Part 4. [1,3] Sigmatropic rearrangements of 4-dimethylaminobutenes and [3,3] sigmatropic rearrangements of 3-dimethylaminohexa-1,5-dienes

Jemison¹,

Ollis²,

Sutherland³

et al. 1980

J. Chem. Soc., Perkin Trans. 1

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Endocyclische S_N‐Reaktionen am gesättigten Kohlenstoff? Vorläufige Mitteilung

Tenud

Farooq

Seibl

et al. 1970

Helvetica Chimica Acta

135

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Fig. 1 illustrates a definition of the terms endocyclic and exocyclic SN‐reactions, referring to intramolecular nucleophilic substitution processes that occur by an SN2‐analogous mechanism. Crossing experiments show that the methyl transfer I → II (see scheme 1) does not follow the formally appealing mechanism of the endocyclic SN‐process III; the reaction proceeds intermolecularly under all conditions investigated. Kinetic measurements indicate that the methyl transfer XI → XII (see scheme 3) occurs in a similar fashion. This behaviour is believed to follow from the preference of tetrahedral carbon for backside attack by the nucleophile in SN2‐reactions. The general experience, according to which intramolecular reaction paths over cyclic transition states with ring sizes of 5 or 6 are preferred to their intermolecular counterparts, is not to be extrapolated to SN2‐reactions at tetrahedral carbon.

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Nuclear‐Spin Polarization in Electron‐Transfer Reactions of Amines

Roth

2006

Helvetica Chimica Acta

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This paper is dedicated to the memory of Professor Hanns Fischer, a pioneer in the chemistry and physics of free radicals, and in designing and adopting magnetic resonance and other physical techniques for their studyChemically induced dynamic nuclear polarization (CIDNP) observed during electron transfer (ET) reactions of tertiary amines such as DABCO (1) or Et 3 N (2) with a wide range of electron acceptors support the involvement of amine radical-cations (e.g., 1C+ or 2C + ) as key intermediates. Radical ions such as 2C + may be deprotonated, generating neutral aminoalkyl radicals (e.g., 2C). When generated by reaction with an electron acceptor of energetically low triplet state such as naphthalene ( 1 Naph*), the resulting pair 2C + /NaphC À reacts mostly by reverse electron transfer (RET) from triplet pairs populating the naphthalene triplet state.The Advent of Chemically Induced Dynamic Nuclear Polarization. -In 1967, the journal Zeitschrift für Naturforschung published two papers from Hanns Fischers laboratory, describing unusual nuclear magnetic resonance (NMR) effects observed during the thermal decomposition of diaroyl peroxides [1]. Only two months later, Ward and Lawler reported related effects observed during rapid reactions of alkyllithium compounds with alkyl halides [2]. These publications introduced the phenomenon of chemically induced dynamic nuclear polarization (CIDNP) to the scientific community. In rapid succession, additional papers appeared reporting CIDNP effects during the thermal decomposition of dialkyl peroxides [3], various photoreactions [4 -7], including reactions of photochemically generated carbenes [5] [7], molecular rearrangements [8], and radical-anion reactions [9].Like many other chemists, we were fascinated by these effects and tried to design systems in which they might be observed to provide mechanistic information. We first studied photoinduced carbene reactions [7] and established that carbene singlet states undergo chlorine abstraction. While this work was in progress, Closs and coworkers [10], and Kaptein and Oosterhoff [11] demonstrated that CIDNP effects are induced in radical pairs; this theory could plausibly rationalize most or all then known effects.At this time, we became interested in photoinduced electron transfer and applied CIDNP to such reactions. Interesting effects observed during the anthraquinone-sensitized cleavage of thymine dimers [12] encouraged us to pursue this research further. We chose photoreactions of carbonyl compounds with amines, which lead to reduction of the carbonyl group or quenching of the excited state without net chemical change as a promising target.

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Nuclear polarization in a thermal 1,3-sigmatropic rearrangement. Evidence for a radical pathway

Cited by 26 publications

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Base catalysed rearrangements involving ylide intermediates. Part 4. [1,3] Sigmatropic rearrangements of 4-dimethylaminobutenes and [3,3] sigmatropic rearrangements of 3-dimethylaminohexa-1,5-dienes

Base catalysed rearrangements involving ylide intermediates. Part 4. [1,3] Sigmatropic rearrangements of 4-dimethylaminobutenes and [3,3] sigmatropic rearrangements of 3-dimethylaminohexa-1,5-dienes

Endocyclische S_N‐Reaktionen am gesättigten Kohlenstoff? Vorläufige Mitteilung

Nuclear‐Spin Polarization in Electron‐Transfer Reactions of Amines

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Nuclear polarization in a thermal 1,3-sigmatropic rearrangement. Evidence for a radical pathway

Cited by 26 publications

References 0 publications

Base catalysed rearrangements involving ylide intermediates. Part 4. [1,3] Sigmatropic rearrangements of 4-dimethylaminobutenes and [3,3] sigmatropic rearrangements of 3-dimethylaminohexa-1,5-dienes

Base catalysed rearrangements involving ylide intermediates. Part 4. [1,3] Sigmatropic rearrangements of 4-dimethylaminobutenes and [3,3] sigmatropic rearrangements of 3-dimethylaminohexa-1,5-dienes

Endocyclische SN‐Reaktionen am gesättigten Kohlenstoff? Vorläufige Mitteilung

Nuclear‐Spin Polarization in Electron‐Transfer Reactions of Amines

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Endocyclische S_N‐Reaktionen am gesättigten Kohlenstoff? Vorläufige Mitteilung