Aldol and Michael reactions

Question 1

what do we get when we subject a ketone to basic conditions

Answer 1

an enolate (ketone with a negative charge at the alpha position)

Question 2

which side of the ketone-enolate equilibrium is favoured under basic conditions

Answer 2

ketone

Question 3

how can we make the ketone-enolate equilibrium favor the enolate

Answer 3

by using a stronger base

Question 4

what do we get when an enolate reacts with an electrophile

Answer 4

electrophilic addition at the alpha position

Question 5

what do we get when the enolate and ketone are mixed together

Answer 5

enolate attacks the ketone, and we get an aldol (new C-C bond made, add the alcohol version of the ketone onto the enolate)

Question 6

what is another name for an aldol

Answer 6

b-hydroxy ketone

Question 7

what is an aldol

Answer 7

an alcohol ketone (a carbonyl with an OH at the beta position)

Question 8

what do we get if an aldol reaction is heated

Answer 8

water is released from the aldol, and we get a double bond between alpha and beta (a,b-unsaturated ketone aka enone)

Question 9

what is an enone

Answer 9

a carbonyl with a double bond between a and b positions

Question 10

what is another name for an enone

Answer 10

a,b-unsaturated ketone

Question 11

what reaction is an enone a product of

Answer 11

aldol condensation

Question 12

T or F: you need heat for aldol condensation

Answer 12

true

Question 13

if there is no heat in the aldol condensation reaction, what type of reaction is it

Answer 13

a simple aldol reaction

Question 14

what is the product of the aldol reaction (give both names)

Answer 14

b-hydroxy ketone

aldol

Question 15

what is the product of the aldol condensation reaction (give both names)

Answer 15

a,b-unsaturated ketone

enone

Question 16

T or F: aldol reactions may be intramolecular

Answer 16

true

Question 17

what are the conditions for the intramolecular aldol reaction

Answer 17

must have at least 2 carbonyls on the molecule, and it would need to form a 5 or 6 membered ring

Question 18

what happens in the crossed aldol reaction (ie what is reacting)

Answer 18

we start with our enolate and react is with an electrophile which is another carbonyl

Question 19

what is one complication with crossed aldol reactions

Answer 19

the second carbonyl may become an enolate itself, and produce a side product known as an enal (a,b-unsaturated aldehyde)

Question 20

what is the product of a crossed aldol reaction when the second carbonyl becomes an enolate itself (give both names)

Answer 20

enal or a,b-unsaturated aldehyde

Question 21

how can we avoid enal production in crossed aldol reactions

Answer 21

we can use a carbonyl that has no alpha hydrogens (because then the molecule cannot be deprotonated to become an enolate)

Question 22

what is the claisen reaction (name the starting product, what is used, and what is produced)

Answer 22

we start with an ester and react it with a base, producing an ester enolate

Question 23

what is the product of an ester reacting with base

Answer 23

ester enolate

Question 24

what is the product when an ester enolate attacks the starting ester

Answer 24

b-keto ester

Question 25

what types of bases are used in the claisen condensation reaction

Answer 25

OR- rather than OH- so we don't get side products

Question 26

T or F: the claisen condensation reaction requires an acid work up (why)

Answer 26

true; it quenches the double enolate formed

Question 27

why doesnt the claisen reaction produce an aldol or an unsaturated double bond?

Answer 27

OCH3- leaves during the mechanism (super important step)

Question 28

how do we create a new C-C bond onto a claisen product

Answer 28

react it with RX (alkylation)

Question 29

what happens when a claisen reaction is heated in acidic conditions

Answer 29

CO2 is released from the b-keto ester = ketone

Question 30

describe the michael reaction

Answer 30

ketone reacts with base and heat to produce an enone

Question 31

what is an enone

Answer 31

a,b-unsaturated ketone

Question 32

T or F: an enone has resonance structures

Answer 32

true

Question 33

what do the resonance structures of an enone show

Answer 33

the b position is electrophilic (positively charged)

Question 34

what happens to an enone in the presence of a nucleophile

Answer 34

nucleophile attack on the b carbon, followed by protonated | beta addition occurs

Question 35

what type of nucleophiles work best in michael reactions

Answer 35

ones that are a resonance stabilized enolate: ie RMgBr or R2CuLi

Question 36

nucleophiles for michael additions are michael (donors/acceptors)

Answer 36

nuc= michael donor

Question 37

electrophiles for michael additions are michael (donors/acceptors)

Answer 37

electrophiles = michael acceptors

Question 38

what type of electrophiles work best for michael reactions

Answer 38

work best when the electrophile is an a,b-unsaturated compound

Question 39

T or F: all electrophiles for michael reactions are carbonyls

Answer 39

false; they don't have to be carbonyls, but they must have resonance

Question 40

T or F: enamines are stabilized enolates (michael donors)

Answer 40

true

Question 41

since enamines are stabilized enolates (michael donors), what can they do?

Answer 41

they can attack a,b-unsaturated compounds (michael acceptors) to produce an iminium salt

Question 42

what will we have to do to the iminium salt produced from the enamine in the michael reaction

Answer 42

quench it because it's a salt (aka hydrolysis)

Question 43

what happens when an iminium salt is hydrolyzed

Answer 43

it reverts to a ketone

Question 44

what is stork enamine alkylation

Answer 44

making use of an enamine to perform 1,4-addition

Question 45

why would we do stork over michael

Answer 45

enolates tend to be poor michael donors, so enamines are better to do the reaction (the products of both will be the same, but the yields and # of side products will differ)