Preparation and facile addition reactions of iminium salts derived from amino ketene silyl acetal and amino silyl enol ether

While iminium salts generated by the oxidation of amino ketene silyl acetals show intriguing reactivities to give useful γ-oxo-α-amino esters via reactions with silyl enol ethers in good yields, new iminium salts are also prepared by the oxidation of amino silyl enol ethers. They undergo facile addition reaction with various nucleophiles to give α-amino ketone derivatives in good yields.

While iminium salts generated from amino ketene silyl acetals react with silyl enol ethers, those from amino silyl enol ethers also undergo facile addition reactions to give alpha-amino ketone derivatives in good yields.

Integrated reactions using addition to conjugated imines and iminium salts

Recently, nucleophilic addition reactions to imino functions have been utilized in many crucial steps for the synthesis of bioactive and functional materials. This article summarizes the integrated “umpolung” reactions of α-imino esters and the use of iminium salts as reactive electrophiles. Regarding the umpolung reactions, the following five reactions are discussed: (1) N-alkylation/homocoupling; (2) tandem N-ethylation/C-allylation; (3) tandem N-ethylation/C-cyanation; (4) reduction of imines with tris(trimethylsilyl)aluminum; and (5) N-alkylation and Claisen rearrangement. Moreover, the generation and reactions of alkoxycarbonyl iminium species are also discussed. These are prepared easily from trisubstituted amino ketene silyl acetals by oxidation, and the subsequent nucleophilic addition of various nucleophiles readily affords the addition products.