Inversion of Reactivity (umpolung) of Carbonyl Compounds Using Organosulfur Compounds Reagents

Organosulfur compounds have been exploited to reverse the reactivity of carbonyl compounds. The heteroatom produces a reactivity pattern in a carbon skeleton. Its electronegativity, being greater than that of carbon (-I effect) and its ability to stabilize an adjacent positive charge (+M effect) makes the sites susceptible to be attacked by reagents possessing a given “philicity”. Nucleophiles attacks the odd C atomes ( 1,3,5... C attack) whereas electrophiles attacks the even C atomes ( 2,4,6... C attack) of the carbonyl compounds. If the reactivity of a carbonyl could be reversed, the acyl carbon would become nucleophilic, and if this transformation can be accomplished, the carbonyl should be regenerated. Seebach termed this process ''umpolung''.