Methods for replacing the carbonyl oxygen by two new substituents (CO→CR1R2) are discussed in this Minireview, whereby R may be H, NR2, alkyl, allyl, benzyl, vinyl, alkynyl, aryl, heteroaryl, or acyl groups. The most frequently used starting materials for geminal disubstitution with the formation of two CC bonds (R1,R2≠H, NR2) are amides and thioamides, which react with organometallic nucleophiles RM (M=Li, MgX, CeX2, TiX3, ZrX3) to give tertiary sec- and tert-alkylamines. Quaternary centers can be built directly from ketones by treatment with Me3Al, MeTiCl3, or Me2TiCl2 (R1R2CO→R1R2CMe2). The scope and limitations of the various methods and mechanistic models are briefly discussed. The remarkable variety and diversity of structures thus accessible are demonstrated by numerous examples.
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