Label cleavage, 3-elimination

Both D-[l- C]xylose and D-[5- C]arabinose were exposed to a concentrated phosphate buffer solution (pH 6.7). 1-Hydroxy-2-propanone (ace-tol) was distilled from the heated solution. Radioassay indicated that similar labeling [3- C] occurred in the acetol from both pentoses, with loss of the configurational difference thus, a 3-ketopentose or its enediol was suggested as an intermediate. Further work with 3-0- and 6-0-methyl-D-glucose and with 1-0-methyl-D-fructose indicated that /3-elimination from a 3-ketose or, in the case of a hexose, from a 3-ketose or a 4-ketose, or both, tautomerization of the resulting a-diketone to a /3-diketone, and hydrolytic cleavage are essential steps in the formation of acetol. 

The dimeric amido complexes underwent reductive elimination after cleavage to form two monomeric, 3-coordinate, 14-electron amido complexes. In the case of the anilido dimer 20, a half-order rate dependence in the palladium complex showed that the reductive elimination occurred after reversible cleavage of the dimer to form two monomers. In the case of the f-butylamido complex 21, rapid reductive elimination occurred after irreversible dimer cleavage. This conclusion was supported by reaction rates that were first order in palladium dimer and by the lack of crossover during the reductive elimination reactions containing two doubly-labeled dimers. 

---