Rearrangement cyclic carbonates

A methylenation of cyclic carbonates such as 6/4-132 using dimethyltitanocene to give a ketene acetal, followed by a subsequent Claisen rearrangement, allowed the synthesis of medium-ring lactones such as 6/4-133 in good yields these are otherwise difficult to obtain. In this transformation, 6/4-133 is formed as a l l-mix-ture of the two atropisomers 6/4-133a and 6/4-133b (Scheme 6/4.33). The substrate... 

Cyclic carbonates react with primary amines to give /3-oxo carbamates which are dehydrated to 2(3//)-oxazolones (equation 141). Thermal rearrangement of the isoxazolone (290) results in the oxazolone (291 equation 142). 

Pyrolysis of the cyclic carbonate at 275 C and atmospheric pressure results in expulsion of carbon dioxide, and the resulting acylnitrenes rearrange to give an almost quantitative yield ofperfluoroalkyl isocyanates 4. Trifluoromethyl, heptafluoropropyl and perfluoroheptyl isocyanates can be prepared by this method. 

Higher-chlorinated camphenes are the most plausible side products. They may be formed together with other cyclic carbon skeletons if the Wagner-Meerwein rearrangement (to polychlorinated bornanes) is hindered [38, 39]. The ionic addition of chlorine to the primary olefinic carbon is always in competition with radical chlorination. Although the first mechanism is more likely, the second one may also take place. It was found that a gentle chlorination of... 

Oxindole, 58, is closely related to the cyclic carbonates and sulfites mentioned above. Pyrolysis of 58 and its homologs proceeds primarily by loss of CO followed by rearrangements and bimolecular reactions. 85,86) The pyrolytic and mass spectrometric reactivity are strikingly parallel in this case, in fact the pyrolytic results prompted a reinterpretation of the oxindole mass spectrum.86)... 

Rearrangements. Cyclic ketones undergo ring expansion on reaction with hydroxyalkyl azides." Regioselectivity is dependent on steric and electronic factors. Beckmann rearrangement of ketoxime carbonates has been observed at room temperature. 

Lactones. Methylenation (Cp2TiMe2 in refluxing toluene) of cyclic carbonates that bear a vinyl group at a carbinolated carbon is followed by a Claisen rearrangement to... 

The cyclic carbonate (134), produced by the addition of vinylene carbonate to phencyclone, loses CO2 on photolysis and rearranges to (135), which is the first... 

Finally, 3-(2ff)-furanones have been obtained by the Pd-catalyzed coupling of 2-methyl-3-butyn-2-ol, CO, CO2, and aryl halides (Eq. 27) [71]. The reaction apparently first generates cyclic carbonates, which rearrange during the reaction. 

The choice of methyl carbonate protection for the C-1 hydroxyl group was inspired by the expectation that upon cleavage of the acetonides, a cyclic carbonate would form spontaneously. Reacetonation of the vicinal glycol then affords the allylic alcohol (132) which is required for the Claisen rearrangement. For this rearrangement, the stereochemical outcome at C-12 of (133) was predictable on the basis of the chair-like transition state in which the bulky cyclic carbonate is equatorially oriented (55). 

White has reported the use of the Claisen rearrangement to implement a ring expansion strategy from the ketene acetal 63 which was generated from cyclic carbonate 62 via Petasis conditions yielding the lactone 64. ... 

A recently-observed nitrogen to carbon acyl migration offers an intriguing opportunity to rearrange cyclic ketones (Scheme 13). ... 

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