Reaction Scheme: 5 CHO NO₂ 6 L-tryptophan H₂O OH do 7 NO₂ Representative procedure for the tryptophan-catalyzed direct aldol reaction Add L-tryptophan (0.02 g, 0.1 mmol) to a suspension of p-nitrobenzaldehyde (0.15 g, 1 mmol), cyclohexanon (0.5 mL, 5 mmol) and water (1 mL, 56 mmol) at room temperature. Stir the reaction mixture until the next la period and quench by adding saturated aqueous ammonium chloride solution (~5 mL). Extract the aqueous solution with dichloromethane (3x5 mL). Dry the combined organic layers with MgSO4 and concentrate on a rotary evaporator. Purify the residue by flash chromatography on silica gel (EtOAc-hexane = 1:3) to give 2- (hydroxy(4-nitrophenyl)methyl)-cyclohexanone as a yellow solid. Questions and tasks: 1. Obtain and interpret a ¹H NMR, IR, and GC-MS for compound 6. 2. Obtain and interpret a mp, ¹H NMR, IR, and GC-MS for compound 7. 3. Write a mechanism that accounts for the formation of the product. Include this in your report discussion. 4. The product obtained in this reaction is the anti aldol product, what would the structure of the corresponding syn aldol look like? 5. Why do you think that p-nitrobenzaldehyde is used rather than say benzaldehyde or p-anisaldehyde (p-methoxybenzaldehyde)?

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Reaction Scheme:
5
CHO
NO₂
6
L-tryptophan
H₂O
OH
7
NO₂
Representative procedure for the tryptophan-catalyzed direct aldol reaction
Add L-tryptophan (0.02 g, 0.1 mmol) to a suspension of p-nitrobenzaldehyde (0.15 g, 1 mmol), cyclohexanone
(0.5 mL, 5 mmol) and water (1 mL, 56 mmol) at room temperature. Stir the reaction mixture until the next lab
period and quench by adding saturated aqueous ammonium chloride solution (~5 mL). Extract the aqueous
solution with dichloromethane (3x5 mL). Dry the combined organic layers with MgSO4 and concentrate on a
rotary evaporator. Purify the residue by flash chromatography on silica gel (EtOAc-hexane = 1:3) to give 2-
(hydroxy(4-nitrophenyl)methyl)-cyclohexanone as a yellow solid.
Questions and tasks:
1. Obtain and interpret a ¹H NMR, IR, and GC-MS for compound 6.
2. Obtain and interpret a mp, ¹H NMR, IR, and GC-MS for compound 7.
3. Write a mechanism that accounts for the formation of the product. Include this in your report
discussion.
4.
The product obtained in this reaction is the anti aldol product, what would the structure of the
corresponding syn aldol look like?
5. Why do you think that p-nitrobenzaldehyde is used rather than say benzaldehyde or p-anisaldehyde
(p-methoxybenzaldehyde)?
Transcribed Image Text:Reaction Scheme: 5 CHO NO₂ 6 L-tryptophan H₂O OH 7 NO₂ Representative procedure for the tryptophan-catalyzed direct aldol reaction Add L-tryptophan (0.02 g, 0.1 mmol) to a suspension of p-nitrobenzaldehyde (0.15 g, 1 mmol), cyclohexanone (0.5 mL, 5 mmol) and water (1 mL, 56 mmol) at room temperature. Stir the reaction mixture until the next lab period and quench by adding saturated aqueous ammonium chloride solution (~5 mL). Extract the aqueous solution with dichloromethane (3x5 mL). Dry the combined organic layers with MgSO4 and concentrate on a rotary evaporator. Purify the residue by flash chromatography on silica gel (EtOAc-hexane = 1:3) to give 2- (hydroxy(4-nitrophenyl)methyl)-cyclohexanone as a yellow solid. Questions and tasks: 1. Obtain and interpret a ¹H NMR, IR, and GC-MS for compound 6. 2. Obtain and interpret a mp, ¹H NMR, IR, and GC-MS for compound 7. 3. Write a mechanism that accounts for the formation of the product. Include this in your report discussion. 4. The product obtained in this reaction is the anti aldol product, what would the structure of the corresponding syn aldol look like? 5. Why do you think that p-nitrobenzaldehyde is used rather than say benzaldehyde or p-anisaldehyde (p-methoxybenzaldehyde)?
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