6-137. The mixed aldol reaction between propionaldehyde (propanal) and acetone gives an 85% yield of 4-hydroxy-2- hexanone when run in THF at -78 °C with lithium diisopropylamide (LDA, a powerful base). The reaction is carried out by first adding the ketone to the base, cooling the solution, and then adding the aldehyde. (a) Why does this mixed system give essentially a single product? (b) Why is there no self-condensation of the acetone? (c) Why does the system not rapidly go on to dehydrate? (d) Why is the ketone added to the base rather than vice versa? ليك debudes for ketones) has no α-hydrogen atoms. This is

6-137. The mixed aldol reaction between propionaldehyde (propanal) and acetone gives an 85% yield of 4-hydroxy-2- hexanone when run in THF at -78 °C with lithium diisopropylamide (LDA, a powerful base). The reaction is carried out by first adding the ketone to the base, cooling the solution, and then adding the aldehyde. (a) Why does this mixed system give essentially a single product? (b) Why is there no self-condensation of the acetone? (c) Why does the system not rapidly go on to dehydrate? (d) Why is the ketone added to the base rather than vice versa? ليك debudes for ketones) has no α-hydrogen atoms. This is

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

Chapter24: Catalytic Carbon-carbon Bond Formation

Section: Chapter Questions

Problem 24.9P

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4- Show how the following compounds could be synthesized starting with dimethyl malonate or ethyl acetoacetate, and any other needed reagents. ore (a) Ph(CH,),CO,H (b)
2 Moin H3C H H₂C C⇒x= base :0: OH Hori H3C H. The aldol reaction is a carbonyl condensation reaction between two carbonyl partners and involves a combination of nucleophilic addition and a-substitution steps. One partner is converted into an enolate ion nucleophile and adds to the electrophilic carbonyl group of the second partner. In the classic aldol reaction, the carbonyl partners are aldehydes or ketones, although aldehydes are more reactive. The product is a B-hydroxy carbonyl compound. Under reaction conditions slightly more vigorous than those employed for the aldol reaction, the ß-hydroxyl group is eliminated in an E1cB dehydration to give an a,ß-unsaturated carbonyl compound. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions H₂C Ἡ :0: heat H Home H3C + H₂O
1a). Plan a synthesis of 3,4-dibromoaniline, starting from benzene. 4steps are required, lists reagents needed and draw in the intermediates.
Why is a strong acid (like HCI) used in a Grignard reaction? O 1) A strong acid is used in the Grignar reaction in order to protonate the carbonyl in order to make a better leaving group, OH. Once teh OH leaves, the alcohol group is reformed due to water. A stable tetrahedral intermediate with a negatively charged oxygen forms O 2) that does not possess a leaving group. This intermediate will exist until a proton source from the strong acid protonates the negatively charged oxygen, affording the neutral alcohol product. 3) The use of a strong acid is not necessary. It is simply recommended as it increases the yield produced in the reaction. 4) The use of a strong acid is necessary for the formation of a Grignard reagent. Without a strong acid, the organomagnesium compound cannot be formed.
2- For the following pairs of compounds, draw their enol tautomers and choose the one the compound that has the greater enol content. (a) 8-6 Å and
8- automerization is a process in which an enol yields a ketone Give one example for a keto to enol tautomerization. Which form is more stable. Also, which is more stable the E isomer or the Z isomer of 2-Chloro, 2-Butene?
18. Identify the products from each step in the following synthesis sequence of reactions. Show the structure of all reactants and products from each step. (a) 3-methyl-1-pentanol + PBr3 --------> A (b) A + Mg/ether-------->B (c) B + 1.CH3CH2C(O)H/2.H3O+ -------> C (d) C + Na2Cr2O7/H2SO4, H2O -----> D
The enolate derived from diethyl malonate reacts with a variety ofelectrophiles (not just alkyl halides) to form new carbon–carbon bonds.With this in mind, draw the products formed when Na+ −CH(CO2Et)2reacts with each electrophile, followed by treatment with H2O.
Treatment of acetylene with a suitable base affords lithium acetylide, which was used as a reagent in a partial synthesis of the antitumor natural product (+)-acutiphycin. (Org. Lett. 2014, 16, 1168-1171) Possible bases to consider H-C=C-H Acetylene Step 1 Li :Base T H-O: Li Lithium hydroxide (LiOH) three steps Lithium acetylide Draw the structure of lithium acetylide. Draw Your Solution di. Η Η Η Η | | | | H-C-C-C-C: II HH HH Butyllithium (BuLi) OR CEC- Li OH CH3 -H CH3 Lithium diisopropyl amide (LDA) OMe H3C H H₂C many steps Li HO OH I (+)-Acutiphycin CH3 CH₂ "OH
2 H3C H3C H C→XT OH H3C The aldol reaction is a carbonyl condensation reaction between two carbonyl partners and involves a combination of nucleophilic addition and a-substitution steps. One partner is converted into an enolate ion nucleophile and adds to the electrophilic carbonyl group of the second partner. In the classic aldol reaction, the carbonyl partners are aldehydes or ketones, although aldehydes are more reactive. The product is a ß-hydroxy carbonyl compound. base :0: OH H H Under reaction conditions slightly more vigorous than those employed for the aldol reaction, the ß-hydroxyl group is eliminated in an E1cB dehydration to give an a,ß-unsaturated carbonyl compound. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instruct ns H3C heat OH H3C :0: H + H₂O H
1. An aldol reaction begins with addition of a catalytic amount of base to an aldehyde or ketone. Write the first step (formation of an enolate) of the reaction when a catalytic amount of NaOH is added to acetaldehyde. Base HH Z H 2. Continue the reaction in problem 1 showing reaction of the enolate with an unaffected molecule of acetaldehyde forming an alkoxide. Subsequent reaction with water yields a B-hydroxyaldehyde. OH -=7 H base H OH o ния H H टे H alo C The overall reaction in problems 1 and 2 is an aldol addition reaction. Each step is reversible. Write the mechanism for the reverse process converting the B-hydroxyaldehyde into two molecules of the original aldehyde. This process is a retro-aldol reaction. Use pK, values to explain why the process is reversible. -OH- e 7L Hlobia. Write the mechanism for reaction of butanone with catalytic aqueous NaOH. (Show each step with a reversible reaction arrow.)
The Zeisel method is an old analytical procedure for determining the number of methoxyl groups in a compound. A weighed amount of the compound is heated with concentrated HI, ether cleavage occurs, and the iodomethane product is distilled off and passed into an alcohol solution of AgNO3, where it reacts to form a precipitate of silver iodide. The Agl is then collected and weighed, and the percentage of methoxyl groups in the sample is thereby determined. For example, 1.06 g of vanillin, the material responsible for the characteristic odor of vanilla, yields 1.60 g of Agl. If vanillin has a molecular weight of 152, how many methoxyl groups does it contain?