CHEMISTRY OF OXAZIRIDINES .12. OXIDATION OF ALKYLIDENETRIPHENYLPHOSPHORANES WITH N-SULFONYLOXAZIRIDINES

The oxidation of alkylidenephosphoranes (ylides) to alkenes and ketones has been explored by Bestmann and co-workers.2Ylides of type 1 (R1= H) gave alkenes while bis(ylides) afforded cycloalkenes. Two molecules of vitamin A were oxidized to /3-carotene by using this methodology. 3z Ketones are formed on oxidation of 1 (R1≠ H) making possible the synthesis of acylsilanes from silyl ylides (R1= ary1, R2= SiMe3).2b,4Triphenyl phosphiteozone (2) was generally used in these oxidations because of its aprotic nature. Although this reagent is readily prepared by treatment of triphenyl phosphite with 03 at -78 °C, it is inconvenient to use because above -35 °C it decomposes to 102 and triphenyl phosphate.5Symmetrical carotenoids have been prepared by oxidation of resonance- stabilized ylides using 50% hydrogen peroxide.6More recently Wassmerman and co-workers reported useful methodology for the preparation 1,2,3-tricarbonyl compounds via oxidation of phosphorane keto ylide carboxylates with ozone or singlet oxygen.7. © 1990, American Chemical Society. All rights reserved.