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17.6 Nucleophilic Addition to a and b -Unsaturated Aldehydes and Ketones

Main Menu. 17.6 Nucleophilic Addition to a and b -Unsaturated Aldehydes and Ketones. Two electron deficient sites. Electron rich (Lewis base, Nu). d -. d +. d +. Electron deficient (Lewis acid, E + ). General Reaction for 1,2-Addition:.

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17.6 Nucleophilic Addition to a and b -Unsaturated Aldehydes and Ketones

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  1. Main Menu 17.6 NucleophilicAddition to a and b-Unsaturated Aldehydes and Ketones Two electron deficient sites Electron rich (Lewis base, Nu) d- d+ d+ Electron deficient (Lewis acid, E+)

  2. General Reaction for 1,2-Addition: Direct Addition (1,2-Addition) and Conjugate Addition (1,4-Addition) 1 1 4 3 2 2 General Reaction for 1,4-Addition: 1 1 4 4 2 Keto-enoltautomerization

  3. Strong nucleophiles favor 1,2-addition. • Nucleophiles that are negatively charged. (more electron rich) • Nucleophiles that are small in size. (the e- density cannot be stabilized.) Selectivity Between 1,2-Addition and 1,4-Addition Examples: RMgX (Grignard reagents), RLi (organolithium), Hydride (LiAlH4, NaBH4, DIBAL) Weak nucleophiles favor 1,4-addition. • Nucleophiles without negative charge. (less electron rich) • Nucleophiles that are larger in size. (the e- density can be stabilized via distribution in a larger space.) Examples: RSH (sulfides), R2CuLi (organocuprate), CN-, amines, halides

  4. major minor Examples of 1,2-Addition >99%

  5. Examples of 1,4-Addition

  6. Nucleophilic Addition to a,b-Unsaturated Carboxylic Acid Derivatives

  7. Original definition: carbon as the nucleophilic atom in a 1,4-addition. Michael Addition Michael acceptor

  8. Main Menu 1. What could be the reagent for the following transformation? Learning Check 2. What should be the major product from the following reaction?

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