Synthesis of unstrained Criegee intermediates: inverse alpha-effect and other protective stereoelectronic forces can stop Baeyer–Villiger rearrangement of gamma-hydroperoxy-gamma-peroxylactones

Vil', V.A.; Barsegyan, Y.A.; Kuhn, L.; Ekimova, M.V.; Semenov, E.A.; Korlyukov, A.A.; Terent'ev, A.O.; Alabugin, I.V.

Авторы: Vil' Vera A., Barsegyan Yana A., Kuhn Leah, Ekimova Maria V., Semenov Egor A., Korlyukov Alexander A., Terent'ev Alexander O., Alabugin Igor V.
Журнал: Chemical science
Том: 11
Номер: 20
Год издания: 2020
Издательство: Royal Society of Chemistry
Местоположение издательства: United Kingdom
Первая страница: 5313
Последняя страница: 5322
DOI: 10.1039/d0sc01025a
Аннотация: How far can we push the limits in removing stereoelectronic protection from an unstable intermediate? We address this question by exploring the interplay between the primary and secondary stereoelectronic effects in the Baeyer–Villiger (BV) rearrangement by experimental and computational studies of γ-OR-substituted γ-peroxylactones, the previously elusive non-strained Criegee intermediates (CI). These new cyclic peroxides were synthesized by the peroxidation of γ-ketoesters followed by in situ cyclization using a BF3·Et2O/H2O2 system. Although the primary effect (alignment of the migrating C–Rm bond with the breaking O–O bond) is active in the 6-membered ring, weakening of the secondary effect (donation from the OR lone pair to the breaking C–Rm bond) provides sufficient kinetic stabilization to allow the formation and isolation of stable γ-hydroperoxy-γ-peroxylactones with a methyl-substituent in the C6-position. Furthermore, supplementary protection is also provided by reactant stabilization originating from two new stereoelectronic factors, both identified and quantified for the first time in the present work. First, an unexpected boat preference in the γ-hydroperoxy-γ-peroxylactones weakens the primary stereoelectronic effects and introduces a ∼2 kcal mol−1 Curtin–Hammett penalty for reacquiring the more reactive chair conformation. Second, activation of the secondary stereoelectronic effect in the TS comes with a ∼2–3 kcal mol−1 penalty for giving up the exo-anomeric stabilization in the 6-membered Criegee intermediate. Together, the three new stereoelectronic factors (inverse α-effect, misalignment of reacting bonds in the boat conformation, and the exo-anomeric effect) illustrate the richness of stereoelectronic patterns in peroxide chemistry and provide experimentally significant kinetic stabilization to this new class of bisperoxides. Furthermore, mild reduction of γ-hydroperoxy-γ-peroxylactone with Ph3P produced an isolable γ-hydroxy-γ-peroxylactone, the first example of a structurally unencumbered CI where neither the primary nor the secondary stereoelectronic effect are impeded. Although this compound is relatively unstable, it does not undergo the BV reaction and instead follows a new mode of reactivity for the CI – a ring-opening process.
Добавил в систему: Астахов Григорий Сергеевич

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Synthesis of unstrained Criegee intermediates: inverse alpha-effect and other protective stereoelectronic forces can stop Baeyer–Villiger rearrangement of gamma-hydroperoxy-gamma-peroxylactonesстатья

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