Temperature and Solvent Control of the Stereoselectivity in the Reactions of Singlet Oxygen with Oxazolidinone-Substituted Enecarbamates

Poon, Thomas; Sivaguru, Jayaraman; Franz, Roberto; Jockusch, Steffen; Martı́nez, Claudia G.; Washington, Ilyas; Adam, Waldemar; Inoue, Yoshihisa; Turro, Nicholas J.

doi:10.1021/ja048438c

Cited by 54 publications

(61 citation statements)

References 15 publications

(14 reference statements)

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“…Their intersection is close to the x-axis and the corresponding H ≠ and S ≠ values have opposite signs. 51,81,88,89,90,210 The observation of such a relationship in the present case indicates that the photooxygenations of investigated enecarbamates 205,207 possess the same reaction mechanism. In Figure 11, the isoselective relationship is depicted.…”

Section: Methodssupporting

confidence: 54%

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Studies in organic and physical photochemistry – an interdisciplinary approach

Oelgemöller

Hoffmann

2016

Org. Biomol. Chem.

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Traditionally, organic photochemistry when applied to synthesis strongly interacts with physical chemistry. The aim of this review is to illustrate this very fruitful interdisciplinary approach and cooperation. A profound understanding of the photochemical reactivity and reaction mechanisms is particularly helpful for optimization and application of these reactions. Some typical reactions and particular aspects are reported such as the Norrish-Type II reaction and the Yang cyclization and related transformations, the [2 + 2] photocycloadditions, particularly the Paternò-Büchi reaction, photochemical electron transfer induced transformations, different kinds of catalytic reactions such as photoredox catalysis for organic synthesis and photooxygenation are discussed. Particular aspects such as the structure and reactivity of aryl cations, photochemical reactions in the crystalline state, chiral memory, different mechanisms of hydrogen transfer in photochemical reactions or fundamental aspects of stereoselectivity are discussed. Photochemical reactions are also investigated in the context of chemical engineering. Particularly, continuous flow reactors are of interest. Novel reactor systems are developed and modeling of photochemical transformations and different reactors play a key role in such studies. This research domain builds a bridge between fundamental studies of organic photochemical reactions and their industrial application.

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Section: Methodssupporting

confidence: 54%

“…This is not the case for the corresponding Z isomers. 207 Using the Eyring relation (equation 3) and a corresponding plot, the enthalpy and the entropy contribution to the free enthalpy G ≠ of the diastereoselectivity are determined.…”

Section: Methodsmentioning

confidence: 99%

Studies in organic and physical photochemistry – an interdisciplinary approach

Oelgemöller

Hoffmann

2016

Org. Biomol. Chem.

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Section: Introductionmentioning

confidence: 99%

“…Moreover, in organic chemistry, solvent‐selective reactions offer unique synthetic methodology . Combining the same reactants in different solvents selectively generates different products . Thus, solvent can be considered as one of the most important stimuli that can direct the course of reactions from one product to another.…”

Section: Introductionmentioning

confidence: 99%

Mesoporous silica supported ytterbium as catalyst for synthesis of 1,2‐disubstituted benzimidazoles and 2‐substituted benzimidazoles

Samanta

Banerjee

Richards

et al. 2018

Applied Organom Chemis

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The benzimidazole ring is an important pharmacophore in contemporary drug discovery. Thus, effort to identifying new compounds containing benzimidazole scaffolds have gained much attention in recent years. In the present study, MCM‐41 type mesoporous silica with large pore (l‐MSN) supported ytterbium was successfully prepared by wet impregnation method. Among rare earth metal salts, ytterbium triflate has already been widely investigated as a catalyst in organic synthesis but less toxic ytterbium oxide has yet to be explored. Relatively high abundance and low cost of ytterbium with respect to many catalytically active metals (e.g. Pd, Au, Ru, Ir, Pt) offer an opportunity to develop sustainable catalysts for organic conversions. The catalyst has been characterized by various techniques including nitrogen adsorption, FT‐IR, TEM, SEM, EDX technique and elemental mapping. The obtained materials exhibit high surface area and a narrow distribution of mesoporosity. The catalytic performance of the Yb@l–MSNs was tested by synthesis of 1,2‐disubstituted benzimidazoles and 2‐substituted benzimidazoles through the coupling of aldehydes with o‐phenylenediamine. The catalyst resulted in excellent yields in short reaction times and the reaction showed tolerance toward both electron‐donating and electron‐withdrawing functional groups at room temperature. A particularly interesting finding was the solvent selectivity of this reaction; namely, 1,2‐disubstituted benzimidazoles generated as major product in water‐ethanol, while the 2‐substituted benzimidazoles was generated exclusively in non‐polar solvents like toluene.

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“…8-10 That is, >98% of the approaching 1 O 2 reacted with one face of the p bond to form one dioxetane product and <2% reacted with the other face to form the other dioxetane product; (b) selectivity in both dioxetane product 3, and in the MDB product 4 is independent of the size of the C-4 alkyl group (Me, i Pr or t Bu) of the enecarbamates; 11,12 (c) the R/S configuration of the MDB product 4 is dependent on the C-4 R/S configuration of the enecarbamates; 11 (d) for the Z-enecarbamates, the selectivity in the dioxetane product 3, is independent of the C-3¢ R/S configuration of the enecarbamates; 10,11,13 (e) the E-isomer shows a solvent and temperature dependence of stereoselectivity in the MDB product 4, in contrast to the corresponding Z-isomer. 11,14, 15 These results raised key questions about the role of the C-4 position and its ability to direct the approach of 1 O 2 -a small eneophile that is blocked to the same extent by substituents of varying size. 11, 12 Consequently, in view of these results, we hypothesized that factors apart from steric ones were playing a crucial role in the observed selectivity.…”

mentioning

confidence: 99%