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2005
Carbohydrates
U 0500
Temperature-Controlled Regioselectivity in the Reductive Cleavage of p-MethAcetals. — The reductive cleavage of the title acetals can lead to
08- 208 oxybenzylidene
exclusive formation of 4-O-Pmb ethers or 6-O-Pmb ethers depending on temperature
and concentration of BH3. For example, 6-O-Pmb ethers are obtained at -78°C under
more dilute conditions. A variety of acid-sensitive functional groups are tolerated under
these conditions. In the presence of proton scavenger the reductive cleavage is greatly
decelerated and yields only 4-O-Pmb ethers. This indicates in situ formation of H+. Additionally, it is shown that reductive cleavage of benzylidene acetals only gives 4-O-Bn
ethers. — (HERNANDEZ-TORRES, J. M.; ACHKAR, J.; WEI*, A.; J. Org. Chem.
69 (2004) 21, 7206-7211; Dep. Chem., Purdue Univ., West Lafayette, IN 47907, USA;
Eng.) — Jannicke
2005
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