Stepwise cycloreversion of oxetane radical cations with initial C-O bond cleavage
Miguel A Miranda1, M Angeles Izquierdo
1Departamento de Química/Instituto de Tecnología Química UPV- CSIC, Universidad Politécnica de Valencia, Camino Vera s/n, Apdo. 22012, 46022, Valencia, Spain. mmiranda@qim.upv.es
Journal of the American Chemical Society
|June 6, 2002
Summary
2,4,6-Triaryl(thia)pyrylium salts facilitate oxetane cycloreversion. The radical cation of 2,3-diphenyl-4-hydroxymethyloxetane undergoes O-C2 cleavage, forming a tetrahydrofuran product within submicroseconds.
Area of Science:
- Photochemistry
- Organic Chemistry
- Reaction Mechanisms
Background:
- 2,4,6-Triaryl(thia)pyrylium salts are established electron-transfer photosensitizers.
- Oxetane ring systems are susceptible to photochemically induced cycloreversion.
- Understanding the fragmentation pathways of substituted oxetanes is crucial for synthetic applications.
Purpose of the Study:
- To investigate the cycloreversion mechanism of 2,3-diphenyl-4-hydroxymethyloxetane using photosensitization.
- To elucidate the intermediate species and fragmentation pathways involved in the photochemical reaction.
- To determine the kinetics of product formation and competing fragmentation routes.
Main Methods:
- Utilized 2,4,6-Triaryl(thia)pyrylium salts as photosensitizers.
- Studied the photochemistry of 2,3-diphenyl-4-hydroxymethyloxetane (1).
- Employed time-resolved spectroscopy to monitor reaction intermediates and kinetics.
Main Results:
- The radical cation of oxetane (1) undergoes stepwise cleavage, initiating with O-C2 bond scission.
- A transient intermediate localizes spin on oxygen and charge on carbon.
- Intramolecular nucleophilic attack leads to the formation of 2,3-diphenyl-4-hydroxytetrahydrofuran (4a) on a submicrosecond timescale.
- Competitive C3-C4 cleavage forms the trans-stilbene radical cation (λmax = 470 nm).
Conclusions:
- The primary photochemical pathway for oxetane (1) involves sequential O-C2 cleavage and intramolecular cyclization.
- The observed kinetics indicate rapid formation of the tetrahydrofuran product.
- The study provides detailed mechanistic insights into photosensitized oxetane cycloreversion.
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