310-24 - Organic Lecture Series CH 310 N LECTURE 24...

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Organic Lecture Series 1 CH 310 N LECTURE 2 4 Textbook Assignment: Chap 19 Finish Homework (for credit): POW 8 posted (Due Mar 28) Today’s Topics: Enolates-conjugate addn & Robinson Ring Notice & Announcements: XM 2 this week Organic Lecture Series 2 Enolate Enolate Anions Anions and and Enamines Enamines Chapter 19
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Organic Lecture Series 3 The acetoacetic ester (AAE) synthesis is useful for the preparation of mono- and disubstituted acetones of the following types CH 3 CC H 2 COEt O O R' 3 HR O 3 H 2 R O A disubstituted acetone A monosubstituted Ethyl acetoacetate (Acetoacetic ester) Acetoacetic Acetoacetic Ester Synthesis Ester Synthesis Organic Lecture Series 4 – consider the AAE synthesis of this target molecule, which is a monosubstituted acetone these three carbons are from ethyl acetoacetate the -R group of a monosubstituted 5-Hexen-2-one O Acetoacetic Acetoacetic Ester Synthesis Ester Synthesis
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Organic Lecture Series 5 – Step 1: formation of the enolate anion of AAE – Step 2: alkylation with allyl bromide COOEt O Et O - Na + O + EtOH Sodium salt of ethyl acetoacetate Sodium ethoxide Eth ano l p K a 15.9 (weaker acid) + + Ethyl acetoacetate p K a 10.7 (stronger acid) O + Br O NaBr + 3-Bromopropene (Allyl bromide) S N 2 + (racemic) Acetoacetic Acetoacetic Ester Synthesis Ester Synthesis Organic Lecture Series 6 – Steps 3 & 4 saponification followed by acidification – Step 5: thermal decarboxylation O 3. NaOH, H 2 O 4. HCl, H 2 O COOH O Et OH + (racemic) OO CO 2 + 5-Hexen-2-one (a monosubstituted acetone) heat Acetoacetic Acetoacetic Ester Synthesis Ester Synthesis
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Organic Lecture Series 7 – to prepare a disubstituted acetone , treat the monoalkylated AAE with a second mole of base, etc COOEt O Et O - Na + + + O Et OH + (racemic) + O CH 3 I O + I - + + S N 2 (racemic) O 3. NaOH, H 2 O 4. HCl, H 2 O O +C O 2 + 3-Methyl-5-hexen-2-one (racemic) (racemic) 5. heat Acetoacetic Acetoacetic Ester Synthesis Ester Synthesis Organic Lecture Series 8 • The strategy of a malonic ester (ME)
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310-24 - Organic Lecture Series CH 310 N LECTURE 24...

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