9: Chemoselectivity
- Page ID
- 23784
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Chemoselectivity is a term that describes the ability of a reagent or intermediate to react with one group or atom in a molecule in preference to another group or atom present in the same molecule. Since most carbohydrate radicals trace their beginnings to reactions involving either a tin-centered [usually Bu3Sn·] or a silicon-centered [usually (Me3Si)3Si·] radical, the chemoselectivity in reactions of these radicals plays a central role in carbohydrate radical formation. An example of a chemoselective reaction is found in Scheme 1, where the tri-n-butyltin radical abstracts the O-thiocarbonyl group from the thioglycoside 1 while the potentially reactive ethylthio group remains in place.1
Chemoselective reaction also can occur when a carbohydrate radical reacts with another molecule present in the reaction mixture. Such a process is shown in Scheme 2, where the pyranos-1-yl radical 2 adds to the C–C double bond in 3 rather that reacting with the chlorine atom or phenylseleno group also present in this molecule (3).2
