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Generation of Secondary, Tertiary, and Quaternary Centers by Geminal Disubstitution of Carbonyl Oxygens

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Abstract

Methods for replacing the carbonyl oxygen by two new substituents (C[DOUBLE BOND]O→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 C[BOND]C bonds (R1,R2≠H, NR2) are amides and thioamides, which react with organometallic nucleophiles R[BOND]M (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 (R1R2C[DOUBLE BOND]O→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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