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Please don’t do problem 31a, but please do problem 32c

Please don’t do problem 31a, but please do problem 32c. Chapter 22 Alpha Substitutions and Condensations of Enols and Enolate Ions. Actually this the chemistry of a- hydrogen atoms. enolate ion. Aldehydes, ketones and esters. IMPORTANT: enolate is a nuke; attacks via of its alpha carbon.

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Please don’t do problem 31a, but please do problem 32c

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  1. Please don’t do problem 31a, butplease do problem 32c

  2. Chapter 22 Alpha Substitutions and Condensations of Enols and Enolate Ions Actually this the chemistry of a-hydrogen atoms enolate ion Aldehydes, ketones and esters IMPORTANT: enolate is a nuke; attacks via of its alpha carbon

  3. Reactions of Enolates with Electrophiles

  4. ALDOL REACTION - Borodin

  5. C

  6. EXAMPLES Dangle the group attached to alpha carbon nuke portion Electrophilic portion

  7. MECHANISM OF ALDOL REACTION + H

  8. In general: Designing Self Aldol Synthesis + break bond; add H to left portion remove H from OH then form C=O

  9. Acid Catalyzed Aldols Also called a,b-unsaturated aldehyde Conjugated enones quite stable

  10. Overall Reaction

  11. Other conditions for dehydration of beta hydroxy aldehydes 1. Base plus heat 2 heat

  12. Planning a Self Aldol synthesis of a,b-Unsaturated aldehyde Add 2 H Add O CH3CH2CH=O CH3CH2CH=O

  13. Aldols Involving Ketones Much slower than aldehydes - need special gimmicks DIACETONE ALCOHOL!!!! mesityl oxide!!!

  14. Crossed Aldol Condensations-Problems Two different aldehydes or ketones PROBLEM - if both have alpha hydrogens

  15. Problem, con’t Also self aldol product of acetaldehyde and propionaldehyde

  16. How to get a single crossed aldol product? Treat one of the aldehydes or ketones with a-hydrogens with another aldehyde or ketone without a-hydrogens. Commonly used carbonyl compouds without a-hydrogens Of course, these will serve as electrophilic centers

  17. Examples Trick is to add compound with a-hydrogen to basic solution containing the compound without a-hydrogen. +

  18. Problem Can the following compound be prepared in good yield by an aldol condensation?

  19. Aldol Cyclizations OH_ OH_ 1,4-diketone Please do problem 22-30

  20. Example 1 Site A to C=O leads to 4-membered ring FAVORED Site B to C=O leads to 6-membered ring

  21. EXAMPLE -2 A C D B D to C=O give 6-membered ring

  22. Example 3

  23. Example Starting diketone? Show the diketone that would give the following 2 H O

  24. Claisen Condensation IMPORTANT POINTS 1. PKA OF ALPHA H’S ON ESTER ARE AROUND 24 (RECALL KETONES ARE AROUND 20. 2. THIS REQUIRES THE USE OF A SLIGHTLY STRONGER BASE USE ALKOXIDES RO- WHERE R IS SAME AS THE OR OF THE ESTER (RECALL PKA OF ALCOHOLS ARE AROUND 17 TO 18.

  25. Claisen CondensationsInvolves Esters with Alpha Hydrogens b-keto ester

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