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DECARBOXYLATION OF b -KETOACIDS

DECARBOXYLATION OF b -KETOACIDS. HYDROLYSIS OF A b -KETOESTER GIVES A b -KETOACID. Claisen Condensation. b -Ketoester. hydrolysis. - CO 2. Ketone. … then, the b -ketoacid decarboxylates in acid. b -Ketoacid. Decarboxylation of a b -Ketoacid. 6-ring. concerted step.

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DECARBOXYLATION OF b -KETOACIDS

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  1. DECARBOXYLATION OF b-KETOACIDS

  2. HYDROLYSIS OF A b-KETOESTER GIVES A b-KETOACID Claisen Condensation b-Ketoester hydrolysis - CO2 Ketone … then, the b-ketoacid decarboxylates in acid b-Ketoacid

  3. Decarboxylation of a b-Ketoacid 6-ring concerted step heat + acid enol tautomerization Carbon dioxide is easily lost since a nice 6-membered ring transition state can be formed for a concerted process. ketone

  4. SYNTHESIS OF KETONES FROM b-KETOESTERS ALKYLATION / DECARBOXYLATION OF b-KETOESTERS

  5. STEP ONE - MAKING THE b-KETOESTER ….. discussed earlier a b-ketoester Claisen condensation a different R group could be used here

  6. STEP TWO - ALKYLATE THE b-KETOESTER a primary halide is best

  7. STEP THREE - HYDROYSIS AND DECARBOXYLATION b-ketoester b-ketoacid this part will be the ketone b-ketoacids decarboxylate easily when heated in acid (see next slide) ketone

  8. ALKYLATION CAN BE SKIPPED an unbranched ketone

  9. DITHIANE ANIONS

  10. - .. C S anion is stabilized by empty 3d orbitals on sulfur Conversion of Aldehydes to Ketones Dithiane Anions a 1,3-dithiane acidic H H2SO4 aldehyde -H2O butyllithium (strong base) various methods .. H2/Ni - or ketone Hg(OAC)2 SN2 H2SO4

  11. PATTERNS

  12. PATTERNS Type of Condensation Reaction b-hydroxy to C=O ALDOL 3-hydroxyaldehyde or (H) 3-hydroxyketone (H) -H2O a,b-unsaturated C=O ALDOL 2-propen-1-al or (with loss of H2O) 2-propen-1-one b-keto ester CLAISEN

  13. PATTERNS CONTINUED b-keto acid DECARBOXYLATION H3O+ heat H3O+ R-X (alkylation) + CO2 from Claisen ketone

  14. SOME OTHER APPLICATIONS

  15. ACYLOIN CONDENSATIONS

  16. Acyloin Condensation Na xylene H2O mechanism not required an acyloin This is a good way to make large rings. High dilution.

  17. A Cyclic Acyloin Condensation Na xylene Zn(Hg) Conc HCl cyclotetratriacontane A VERY BIG RING !

  18. PATTERN a-hydroxyketone ACYLOIN an acyloin

  19. CATENANES

  20. Catenanes Interlocked rings.

  21. HELL-VOLHARD-ZELINSKY a-BROMOACIDS AND a-BROMOESTERS

  22. Hell-Volhard-Zelinsky Reaction 1) P, Br2 2) H3O+ a-bromoacid PBr3 H3O+ (workup step) Acid halides have a larger enol content than ketones. .. : Double bonds react with bromine! Resonance increases the electron density in the double bond. Enols are more reactive than alkenes.

  23. Synthesis of Aminoacids and a-Hydroxyacids neutralization step not shown + phenylalanine NaOH lactic acid

  24. REFORMATSKY REACTION A COUSIN TO THE GRIGNARD REACTION

  25. Reformatsky Reaction Fischer Esterification or via the acid chloride a-bromoester Zn, ether 1) Reformatsky reagent 2) H3O+ Reacts like a Grignard reagent!

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