Cyclobutene ozonide

Cyclobutene ozonide <88JST(190)125> revealed a long O—O bond of 1.492 A relative to cyclopen tene ozonide (1.475 A) <83JPC538l> and also a smaller C—O—C angle of 94.0° compared with... 

The double )5-scission pathway becomes dominant in bicyclic systems (Equations (7)-(9) and Scheme 13). Thus, cyclopentene ozonide (69) gives cyclopropane (Equation (7)) <68TL329l>. Photolysis of the ozonide derived from 1,4-benzodioxins (70) provides a method for the preparation of labile o-benzoquinones (71) (Scheme 13) <87JOC56l6>. Photolysis can also provide a route to unstable compounds and transient species such as the aziridine-2,3-dione (72) (Equation (8)), identified at 77 K using infrared spectroscopy <80JA6902>. Relatively unstable azacarbapenems (73) have been prepared by photolysis of tricyclic compounds containing a cyclobutene ozonide (Equation (9)). On silica, the 1,2,4-trithiolane (74) underwent photo-equilibration (Equation (10)) with the 1,3-dithetane (75) and sulfur. 

A number of the bicyclic ozonides 12 were prepared in good yield (45-65 %) by diimide reduction of furan singlet oxygenates (Eq. 9) 23>. Again, low temperature were essential because the furan endoperoxides readily transform into 1,2-diacyl-ethylenes. Of course, the bicyclic ozonides 12 can alternatively be prepared via ozonolysis of the appropriate 1,2-disubstituted cyclobutene 24). 

Cyclobutenes have been applied as latent functionality of 1,4-dicarbonyl systems. Photolysis of (466) gave a 1.5 1 mixture (60%) of (467a) and (467b), which were cleaved by ozone and subsequent reduction of the ozonides yielded the epimeric (468). Cyclization and dehydration process converted (468) to the furan (469) 160). Furan (469) was converted to hibiscone C in a few steps, 60). 

The structure of the ozonides of the simplest unsaturated cyclic hydrocarbons can be elucidated based on the rotational spectra of the FOZ and its isotopomers, such as species singly enriched with H, or 0 or multiply enriched with 0. Thus, the FOZ of cyclobutene has structure 293, of Cj symmetry, with the 00 bridge slightly longer than that of the FOZ of ethylene, to accommodate some ring tension . The microwave spectra of the FOZ of cyclopentene point to a ground state of structure 294, of Cj symmetry, with the OO bridge in the endo conformation . ... 

Partially fluorinated cyclobutene gives at 0 C an ozonide that is stable in dichloromethane solution at room temperature.86 It is decomposed by acid hydrogen peroxide yielding fluorinated butanedioic acid.86 Bubbling ozone into a pentane solution of hexakis(trifluoro-methyl)benzvalene gives a pale-yellow ozonide which is stable at room temperature (Table 5).87... 

The 1,3-dipolar addition of ozone to hexamethyl Dewar benzene gives the corresponding ozonide, which is photolytically converted to tetramethylcyclobutadiene (57)S9>. The photochemical addition of benzaldehyde to hexamethyl Dewar benzene yields a (2+2)cycloadduct the oxetan part of which is reduced much more rapidly than the cyclobutenic double bond. This may be due to the high substitution around the double bond (58) 60). 

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