羰基的保护方法.pdfVIP

9924 J. Org. Chem. 1998, 63, An Efficient Photo-SET-Induced Cleavage of DithianeCarbonyl Adducts and Its Relevance to the Development of Photoremovable Protecting Groups for Ketones and Aldehydes William A. McHale and Andrei G. Kutateladze* Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80208 Received August 20, 1998 Irradiation of dithianealdehyde/ketone adducts in the presence of benzophenone leads to CC bond cleavage regenerating the carbonyl compounds. It is established that the mechanism of this reaction involves photochemically induced single electron transfer from the dithiane moiety to the excited molecule of ET-photosensitizer, accompanied by mesolytic CC cleavage in the generated cation-radical, which is assisted by the anion-radical of benzophenone. This mechanism is confirmed by a Hammett plot study of the cleavage in the dithiane adducts of substituted aromatic aldehydes and a deuterium kinetic isotope effect study. Ab initio computations at UHF/6-31G* and MP2/6- 31G* levels of theory in conjunction with self-consistent reaction field (self-consistent isodensity- polarized continuum model), to account for the solvent effect, also support the experimental findings. The reaction is most efficient for protection of aromatic aldehydes and ketones and aliphatic ketones, and is a novel method for protecting carbonyl functionalities with a photoremovable group. Introduction One significant problem with this method is that carbo-