Synthesis and Reactivity of Dipole-Stabilized but Unchelated α-Aminoorganolithiums

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Abstract
Two N-methyl-5-lithio-2-pyrrolidinones have been prepared by tin-lithium exchange. These two alpha-aminoorganolithium compounds that are stabilized by an amide dipole, but not by chelation to the amide carbonyl. Both constitute test cases for comparing the stability and reactivity of "dipole-stabilized" and "unstabilized" alpha-aminoorganolithiums. We find that active methylene protons interfere with the reaction, so geminal disubstitution alpha to the amide carbonyl was necessary to suppress side reactions. These species do not react as efficiently as unstabilized alpha-aminoorganolithiums, or even as well as chelated dipole-stabilized alpha-aminoorganolithiums, toward typical electrophiles. The tin-lithium exchange to form these species was also not as facile as with other alpha-aminoorganostannanes.