Length Matters: One Additional Methylene Group in a Reactant is Able to Affect the Reactivity Pattern and Significantly Increase the Product Yield

The outcome of the nucleophilic opening of 3- O -benzoyl-β- d -arabinofuranose 1,2,5-orthobenzoate with 4-(ω-chloroalkoxy)phenols (SnCl 4 , CH 2 Cl 2 , –25 °C) unusually strongly depends on the length of the methylene chain of the nucleophile. The presence of one extra methylene group in the molecule of 4-(3-chloropropoxy)phenol [as compared to 4-(2-chloroetoxy)phenol] results in four-fold reduction in the reaction time and five-fold increase in the yield of a selectively protected monosaccharide glycoside with a hydroxy group at C-5, which is a valuable building block for the synthesis of oligoarabinofuranosides related to mycobacterial arabinans. Possible reasons and consequences of this finding are discussed.