The Claisen condensation converts two molecules of an ester into a B-keto ester. The reaction starts with the ester in an alkoxide/alcohol solution and is worked up with acid to form the neutral B-keto ester product. 1. "OCH,CH3/ CH3CH2OH 2. H3O* Show the curved-arrow mechanism for the Claisen condensation of ethyl ethanoate treated with ethoxide ion. Include all formal charges and nonbonding electrons. In each step, draw only the species that react in that step. If an enolate resonance form is possible, draw only the carbanionic form. If a CHx group is being deprotonated, draw all H's on the reacting site. Tip: always omit ethanol byproducts. Step 1c: Draw the structure(s) resulting from the curved arrow mechanism of step 1. Include formal charges and all hydrogen atoms, but do not include lone pairs. Draw the structure(s) indicated by the curved-arrow mechanism. H,C CH3 H,C CH, Incorrect

The Claisen condensation converts two molecules of an ester into a B-keto ester. The reaction starts with the ester in an alkoxide/alcohol solution and is worked up with acid to form the neutral B-keto ester product. 1. "OCH,CH3/ CH3CH2OH 2. H3O* Show the curved-arrow mechanism for the Claisen condensation of ethyl ethanoate treated with ethoxide ion. Include all formal charges and nonbonding electrons. In each step, draw only the species that react in that step. If an enolate resonance form is possible, draw only the carbanionic form. If a CHx group is being deprotonated, draw all H's on the reacting site. Tip: always omit ethanol byproducts. Step 1c: Draw the structure(s) resulting from the curved arrow mechanism of step 1. Include formal charges and all hydrogen atoms, but do not include lone pairs. Draw the structure(s) indicated by the curved-arrow mechanism. H,C CH3 H,C CH, Incorrect

Organic Chemistry

8th Edition

ISBN:9781305580350

Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote

Publisher:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote

Chapter16: Aldehydes And Ketones

Section: Chapter Questions

Problem 16.26P: Wittig reactions with the following -chloroethers can be used for the synthesis of aldehydes and...

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H₂C OEt H₂C OEt 1. NaOEt, EtOH 2. H₂O* H₂C EtOH OEt Esters, like aldehydes and ketones, are weakly acidic. Treatment of an ester with 1 equivalent of a strong base, such as sodium ethoxide, causes a reversible carbonyl condensation to occur that forms a ẞ-ketoester. This reaction is known as the Claisen condensation. The tetrahedral intermediate thus formed expels an alkoxide leaving group to give an acyl substitution product, a ẞ-ketoester. The steps leading up to this point are all reversible. The best yields for the Claisen condensation are obtained when the starting ester has more than one acidic a-hydrogen. In these cases, a second deprotonation of the a-carbon drives the reaction equilibrium toward the product, thus requiring a full equivalent of base instead of a catalytic amount. Subsequent protonation with dilute aqueous acid resultsn a high yield of the final product. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing…
H3C OH 1. Br2, PBг3 2. H₂O H3C OH Br The a-bromination of carbonyl compounds by Br₂ in acetic acid is limited to aldehydes and ketones because acids, esters, and amides don't enolize to a sufficient extent. Carboxylic acids, however, can be a-brominated by first converting the carboxylic acid to an acid bromide by treatment with PBr3. Following enolization of the acid bromide, Br2 reacts in an a-substitution reaction. Hydrolysis of the acid bromide completes the reaction. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions Br Br зь P-Br Br H₂C H₂C SH Br Br
1. Br₂, PBrg 2. H₂O H₂C OH H3C OH Br The a-bromination of carbonyl compounds by Br₂ in acetic acid is limited to aldehydes and ketones because acids, esters, and amides don't enolize to a sufficient extent. Carboxylic acids, however, can be a-brominated by first converting the carboxylic acid to an acid bromide by treatment with PBr3. Following enolization of the acid bromide, Br₂ reacts in an α- substitution reaction. Hydrolysis of the acid bromide completes the reaction. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions H3C :0: :0::Br: Br Br H3C CO-P H Br Br
Nucleophilic addition-elimination reactions, Part 2 1. Draw a complete, arrow-pushing mechanism that shows the product from each of the following reactions. CH,CH,0° CH;CH;OH CH,0° H* (cat) CH;OH OH 2. The tetracyclic molecule (+)-fawcettimine is an interesting synthetic challenge. One synthesis begins with a Michael addition reaction followed by an annulation reaction and subsequent decarboxylation. Show the complete, arrow-pushing mechanism for these reactions. но 3. Propose a forward synthesis to achieve the retrosynthesis shown below.
Choose the BEST reagent for carrying out the following conversion. or H (A) NaOH, H₂O B) NaBH4 C CH₂PPh3 All of the above CH₂OH
Show the mecanism for the protection of the diol by forming an acetal with acetone. Remember this reaction occurs in an acidic environment CH3 CH3 с H D CH,COCH; tocamobor CH3 Н.С. OH B 10 11
11. What products are formed when the following ester is hydrolyzed with water and H,SO4? CH,CH,CHS A) CH;CH2CH,CH(CH3)2 + CO2 В) CН:CH:CH.СОН + НОСН(CH)2 C) CH;CH2CHCOOH + HOCH(CH:)2 D) CH:CH-CH-СООН + НООСН(СН)2 OCH(CH2
OH pyridine 1. SOCI, SO2 Br DMSO / H20 2. N-Br OH N-H a = Proton transfer d = El Elimination f = Syl Nucleophilic substitution b = Lewis acid/base e = E2 Elimination g = Sy2 Nucleophilic substitution c = Electrophilic addition The rections above involve synthesis or reactions of alcohols and ethers. Identify the mechanism by which they proceed from among the mechanisms listed. Use the letters a - g for your answers. 1. 2.
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H3C. H3C. CH3 nnc» XT :OH 2 CH₂OH HCI catalyst Aldehydes and ketones react reversibly with two equivalents of alcohol in the presence of an acid catalyst to give acetals. Alcohols are poor nucleophiles, and so protonation of the carbonyl oxygen is used to make the carbonyl carbon a stronger electrophile. Addition of the first equivalent of alcohol gives a hemiacetal, a hydroxyether. Addition of the second equivalent of alcohol is accompanied by loss of water to yield the product acetal. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions CH3 H3C CH3OH H3CQ OCH3 CH3 H3C. H HO: :OCH 3 CH3 46
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