Physical and chemical quenching rates and their influence on stereoselective photooxygenation of oxazolidinone-functionalized enecarbamates.
نویسندگان
چکیده
Physical and chemical quenching rate constants were measured for the reaction of singlet oxygen with oxazolidinone-functionalized enecarbamates to investigate the role of vibrational deactivation in product stereoselectivity.
منابع مشابه
Stereoselective E/Z photoisomerization of oxazolidinone functionalized enecarbamates: direct and triplet sensitized irradiation.
Oxazolidinone-functionalized enecarbamates undergo diastereoselective E/Z photoisomerization upon direct and triplet sensitized irradiations with chiral/achiral sensitizers, showing that the enhanced product diastereoselectivity depends on the solvent and temperature.
متن کاملTemperature and solvent control of the stereoselectivity in the reactions of singlet oxygen with oxazolidinone-substituted enecarbamates.
Oxazolidinone-functionalized enecarbamates react stereoselectively with singlet oxygen to give methyldesoxybenzoin (MDB) in moderate to high enantiomeric excess. The stereochemical outcome depends on the E/Z substrate geometry, temperature, and solvent variables. The analysis of the differential activation parameters suggests a large contribution from the entropy term in determining the enantio...
متن کاملThe reaction of singlet oxygen with enecarbamates: a mechanistic playground for investigating chemoselectivity, stereoselectivity, and vibratioselectivity of photooxidations.
Photochirogenesis, the control of chirality in photoreactions, is one of the most challenging problems in stereocontrolled photochemistry, in which the stereodifferentiation has to be imprinted within the short lifetime of the electronically excited state. Singlet oxygen (1O2), an electronically excited molecule that is known to be sensitive to vibrational deactivation, has been selected as a m...
متن کاملHighly diastereoselective dioxetane formation in the photooxygenation of enecarbamates with an oxazolidinone chiral auxiliary: steric control in the [2 + 2] cycloaddition of singlet oxygen through conformational alignment.
The photooxygenation of oxazolidinone-substituted enecarbamates leads to diastereomerically pure dioxetanes. The high diastereoselectivity is rationalized in terms of effective pi-facial control achieved by shielding one side of the double bond with the chiral auxiliary. The absolute configuration of the dioxetanes is assigned by derivatization to diols.
متن کاملStereocontrol within confined spaces: enantioselective photooxidation of enecarbamates inside zeolite supercages.
Dye-exchanged Y zeolite is shown to be an effective medium to control the stereoselectivity in the photooxygenation of chiral oxazolidinone-functionalized Z/E-1 enecarbamates. An enantioselectivity (ee) as high as 80% was observed in the methyldesoxybenzoin (MDB) product, obtained in the methylene-blue-exchanged NaY zeolite at room temperature. The efficacy of the asymmetric induction in the MD...
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ورودعنوان ژورنال:
- Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology
دوره 8 7 شماره
صفحات -
تاریخ انتشار 2009