In a Communication entitled "HIO3 and I2O5: Mild and Selective Alternative Reagents to IBX for the Dehydrogenation of Aldehydes and Ketones",[1] K. C. Nicolaou et al. disclosed new reagents, HIO3·DMSO and I2O5·DMSO complexes for the dehydrogenation of ketones and aldehydes to afford the corresponding enones and enals, respectively. The reagents were prepared by heating either iodic acid (HIO3), or iodine pentoxide (I2O5) in DMSO (1 M solution) for 80 °C for 1 h. This solution thus prepared was then diluted with cyclohexene as co-solvent and employed in the oxidation of a ketone or enone at 45–65 °C. The authors undertook a large series of such reactions on small scale (0.1–0.5 mmol), and also on many occasions made the reagents on a larger scale (up to 2.5 mmol), without incident. Dr. S. Woodward (University of Nottingham) has subsequently reported to them (personal communication) that during the preparation of HIO3·DMSO on a 42 mmol scale, after 30 min heating at 80 °C, the reaction exploded. The reaction was being stirred using a circulator–heater equipped with a safety cut-out so accidental overheating could be eliminated as cause. No abnormalities were found in the reagents employed. The authors would like to direct the attention of the reader to the adverse incident reported by Dr. S. Woodward and urge extreme caution in the large-scale implementation of the procedure for making HIO3·DMSO. Until further investigation is completed they suggest the same caution should be applied to the synthesis of the I2O5·DMSO complex. [1] K. C. Nicolaou, T. Montagnon, P. S. Baran, Angew. Chem. 2002, 114, 1444; Angew. Chem. Int. Ed. 2002, 41, 1386. |
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