Mechanistic studies on PET-oxidative cyclization of unsaturated silyl enol ethers: dependence of the regioselectivity on alcohol addition and pressure effects

Ackermann, Lutz; Heidbreder, Andreas; Wurche, Frank; Klärner, Frank‐Gerrit; Mattay, Jochen

doi:10.1039/a807683i

Cited by 19 publications

(9 citation statements)

References 22 publications

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“…On the other hand the radical center of the distonic radical 49 may add vinylogously to the cationic center resulting in the non‐distonic radical cation 51 which is identical to the radical cation 47 of the silyl enol ether 46 . Analogous to our former published results this radical cation should cyclise predominantly in an endo fashion if not suppressed by steric effects 28–31…”

Section: Resultssupporting

confidence: 85%

“…For example, silyl enol ether radical cations (e.g. 47 ) predominately cyclize in a 6‐ endo fashion, as we have shown in former studies 28–31. By addition of strong nucleophiles such as alcohols the endo / exo product ratio can be lowered due to the fast cleavage of the formal trimethyl silyl cation; this results in the α‐carbonyl radical 48 which cyclises predominately in a 5‐ exo mode (Scheme ) 28–31…”

Section: Resultsmentioning

confidence: 82%

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Studies on azaspiracid biotoxins. I. Ultrafast high‐resolution liquid chromatography/mass spectrometry separations using monolithic columns

Volmer

Brombacher

Whitehead

2002

Rapid Comm Mass Spectrometry

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In this study, the performance of monolithic columns was evaluated for ultrafast liquid chromatography/mass spectrometry (LC/MS) analyses and for high-resolution separations of several azaspiracid biotoxin analogs. Because of their high permeability, monolithic columns offer a number of advantages over conventional packed columns; viz., very low backpressures and relatively flat van Deemter curves at high flow rates. That is, very high flow rates can be used for ultrafast analyses or, by using longer than normal columns, high-resolution separations are possible. In a series of experiments, we varied the mobile phase flow rates between 1 and 8 mL/min, and studied their impact on chromatographic parameters such as retention time, resolution, number of plates and pressure. The chromatographic run times could be reduced to ca. 30 s without a significant change in the separation efficiency. A signal intensity comparison revealed interesting differences between atmospheric-pressure chemical ionization (APCI) and electrospray ionization (ESI) in their flow-rate dependency. An explanation with respect to the behavior as of a mass-flow or a concentration-dependent device is given in the paper. Additionally, the column length was varied between 10 and 70 cm. As a result, the number of theoretical plates increased substantially. In the example shown in the report, an increase from 13 000 plates for a 10-cm column to 80 000 for a 70-cm column is demonstrated. In addition, the potential of the monolithic columns for high-resolution LC/MS separations is shown for a complex biotoxin mixture, which was separated on a 40-cm-long column.

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Section: Resultssupporting

confidence: 85%

Section: Resultsmentioning

confidence: 82%

Studies on azaspiracid biotoxins. I. Ultrafast high‐resolution liquid chromatography/mass spectrometry separations using monolithic columns

Volmer

Brombacher

Whitehead

2002

Rapid Comm Mass Spectrometry

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“…, 163 (3), 162 (21), 161 (8), 149 (7), 148 (50), 147 (31), 146 (10), 145 (8), 144 (6), 143 (4), 135 (3), 134 (19), 133 (29), 132 (3), 131 (6), 130 (11), 129 (5), 121 (5), 120 (12), 119 (16), 118 (4), 117 (10), 115 (4), 108 (6), 107 (8), 106 (14), 105 (29), 104 (31), 103 (6), 96 (3), 95 (30), 94 (16), 93 (22), 92 (37), 91 (100), 81 (17), 80 (23), 79 (65), 78 (26), 77 (48), 68 (3), 67 (19), 66 (7), 65 (16), 55 (11), 54 (3), 53 (13), 52 (4), 51 (7), 43 (4), 42 (4), 41 (39), 40 (4), 39 (21) …”

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Synthetic Applications in Radical/Radical Cationic Cascade Reactions

Rinderhagen

Mattay

2004

Chemistry A European J

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Oxidative photoinduced electron transfer (PET) reactions have been performed with various cyclic cyclopropyl(vinyl) silyl ethers bearing an olefinic or acetylenic side chain. The reactions result in bi- to tetracyclic ring systems via a fragmentation-radical/radical cationic addition reaction pathway with well defined ring juncture. The mode of cyclisation (endo/exo) can be partially controlled by addition of nucleophiles due to the suppression of radical cationic reaction pathways. Quantum chemical calculation of the cyclisation transition states underline the experimentally found selectivities. Additional mechanistic studies concerning the saturation step reveal that the final radical is saturated mostly by the solvent and traces of water in the solvent.

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“…During the last decade, photoinduced electron transfer (PET) has become successfully established in organic synthesis 18–20. Radical ions can easily be generated by oxidative21–23 or reductive24–27 single‐electron transfer (SET) from neutral compounds. An alkyne‐carbonyl cyclization reaction, for example, was used to prepare bicyclic tertiary cycloalkanols by photoreductively induced electron transfer from triethylamine (TEA) as a strong reducing agent in acetonitrile or by photoionization in pure hexamethylphosphoric triamide (HMPA) 28,29.…”

Section: Introductionmentioning

confidence: 99%

Photoreactions of Tricyclic α‐Cyclopropyl Ketones and Unsaturated Enones – Synthesis of Polyquinanes and Analogous Ring Systems

Tzvetkov¹,

Neumann²,

Stammler³

et al. 2006

Eur J Org Chem

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Polycyclic systems of both angular and propellane type have been synthesized through intramolecular radical cyclization reactions, by photochemically induced electron transfer of tricyclic α‐cyclopropyl ketones or by photolysis of unsaturated enones. In general, tricyclic α‐cyclopropyl ketones, each bearing an alkynyl or alkenyl side chain at the position γ to the carbonyl group, were used as starting materials. The reactions resulted in regioselective cleavage of one cyclopropyl bond with formation of tri‐ to tetracyclic ring systems by a tandem fragmentation‐radical/radical anionic reaction pathway. The regioselectivity of the cyclization (exo/endo) depends on the length of the unsaturated side chain. In cases involving α‐cyclopropane derivatives with alkoxymethyl side chains, various non‐cyclization processes were observed. In addition, the photoinduced cyclization of the corresponding bicyclic enone derivatives with the same unsaturated side chains afforded tetra‐ and tricyclic products of propellane type in good yields and with high stereoselectivity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

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Mechanistic studies on PET-oxidative cyclization of unsaturated silyl enol ethers: dependence of the regioselectivity on alcohol addition and pressure effects

Cited by 19 publications

References 22 publications

Studies on azaspiracid biotoxins. I. Ultrafast high‐resolution liquid chromatography/mass spectrometry separations using monolithic columns

Studies on azaspiracid biotoxins. I. Ultrafast high‐resolution liquid chromatography/mass spectrometry separations using monolithic columns

Synthetic Applications in Radical/Radical Cationic Cascade Reactions

Photoreactions of Tricyclic α‐Cyclopropyl Ketones and Unsaturated Enones – Synthesis of Polyquinanes and Analogous Ring Systems

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