Carbonyl chemistry- Aldol derivatives

Question 1

When can an intramolecular aldol occur

Answer 1

1. Where a molecule contains 2 ketones

Question 2

What happens in intramolecular adols

Answer 2

1. An enol/enolate forms
2. Then it quickly reacts with a ketone
3. Forms a ring

Question 3

What size ring will form

Answer 3

1. 5 or 6 membered rings are preferred- bond angles good, no strain- low energy
2. 3,4- too highly strained
3. 7,8+ - too big

Question 4

What is a problem with intramolecular aldols

Answer 4

1. Systems that contain 2 ketones that are the required distance apart are not that common

Question 5

What is Robinson annulation

Answer 5

1. 2 step process for forming 6-member rings
2. 2 new C-C bonds formed in 2 distinct steps
3. 3 Separate mechanism operate

Question 6

What are the 3 separate mechanisms present in Robinson annulation

Answer 6

1. Michael/conjugate addition
2. Intramolecular aldol
3. Dehydration

Question 7

What is the Claisen reaction

Answer 7

1. Close relative of aldol
2. Formally a way of acylating the beta-carbon
3. classically condensation between 2 ester molecules under basic conditions
4. Can do same with ketone and ester electrophile
5. First an enolate is formed which is then acts as a nucleophile to the ester electrophile

Question 8

What does Claisen reaction between 2 esters produce

Answer 8

1. Beta-keto ester

Question 9

What does Claisen reaction between ketone and ester produce

Answer 9

1. 1,3-diketone

Question 10

What esters are useful to use in Claisen reaction

Answer 10

1. Non-enolisable esters- oxalate, formate, carbonate, benzoate
2. Can’t do side reactions
3. Act as the electrophile

Question 11

What is a Dieckmann condensation

Answer 11

1. An intramolecular Claisen reaction
2. Useful for forming rings
3. Forms when 2 ester groups present
4. Produces cyclic beta-keto ester

Question 12

What is a Knoevengal reaction

Answer 12

1. Aldol condensation between 1,3-dicarbonyls (enolate nucleophile) and aldehydes and ketones (electrophile)

Question 13

Why is Knoevengal reaction useful

Answer 13

1. Specific enolate equivalent used

2. Don’t need to worry about temperature or dry conditions

Question 14

What base is used for the Knoevengal reaction and when does this change

Answer 14

1. Amines base of choice, usually buffered with aceitic acid
2. Choice of amine changes mechanism
3. Primary/secondary form iminium with aldehyde or ketone
4. Tertiary don’t