091ChemInform Abstract Photolysis of the galactopyranose (I) in alkaline (NaOH or MeO-) methanol under nitrogen affords the alcohol (II) quantitatively. Amines also promote the reaction, and the efficiency of removal of the tosyloxy group depends upon the structure of the particular amine (DABCO, Et3N, iPr2NEt, tBuNH2). No correlation is observed between the nucleophilicity of the bases and the efficiency of reaction. However, a qualitative correlation is found with the electron-donating ability of the amines (which is related to their ionization potentials). Direct evidence for electron transfer is obtained by examining the flash photolysis of tosylate (I) in the presence of amine donors leading to the tosylate radical anion and the amine radical cation; the former undergoes fission to Tos• + alkoxide anion -OR. This electron transfer mechanism is of practical use as is demonstrated by photolysis of the allofuranoses (III). The nitro-derivative (IIIa) yields both the deprotected carbohydrate (IV) and its epimerized isomer (V) via a radical mechanism whereas the tosyl-derivative (IIIb) yields only the deprotected product (IV) without epimerization. Preliminary experiments with other electron transfer sensitizers have been unsuccessful.
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