Silyl enol ether formation Mannich reaction

The best catalyst for this transformation was AgSbFg (10 mol%), and (3-ketoesters, malonates, and silyl enol ethers have been used for the nucleophilic addition on the pyridinium intermediate DD. The dihydroisoquinolines 48 have been further used in several reactions in order to assemble the framework of various alkaloids. One example is given in the formation of dihydroisoquinoline 49, bearing a pendent a, 3-unsaturated ketone. Compound 49 can rearrange to the tetracycle 50 (related to the core structure of karachine, Scheme 5.23), using TMSOTf, via a tandem Michael addition-Mannich reaction process (intermediates EE and FF). 

Silyl enol ethers serve as precursors to a variety of -(substituted methyl) ketones (Scheme 54). Trimethylsilyl trifluoromethanesulphonate catalyses the formation of a-alkoxymethyl ketones from dialkoxymethanes in the presence of a sterically hindered nitrogen base, and titanium tetrachloride catalyses the site-specific ureidoalkylation of silyl enol ethers of cycloalkanones by reaction with chloromethyl carbamates. Mannich dimethylaminomethylation can be... 

One of the important C-C bond forming reactions, for the formation of P-amino-ketones and -aldehydes, involves the Mannich-type reaction between preformed imines and silyl enol ethers. 

Besides the allylation reactions, imines can also undergo enol silyl ether addition as with carbonyl compounds. Carbon-carbon bond formation involving the addition of resonance-stabilized nucleophiles such as enols and enolates or enol ethers to iminium salt or imine can be referred to as a Mannich reaction, and this is one of the most important classes of reactions in organic synthesis.104... 

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