Aldol and Michael reactions Flashcards
what do we get when we subject a ketone to basic conditions
an enolate (ketone with a negative charge at the alpha position)
which side of the ketone-enolate equilibrium is favoured under basic conditions
ketone
how can we make the ketone-enolate equilibrium favor the enolate
by using a stronger base
what do we get when an enolate reacts with an electrophile
electrophilic addition at the alpha position
what do we get when the enolate and ketone are mixed together
enolate attacks the ketone, and we get an aldol (new C-C bond made, add the alcohol version of the ketone onto the enolate)
what is another name for an aldol
b-hydroxy ketone
what is an aldol
an alcohol ketone (a carbonyl with an OH at the beta position)
what do we get if an aldol reaction is heated
water is released from the aldol, and we get a double bond between alpha and beta (a,b-unsaturated ketone aka enone)
what is an enone
a carbonyl with a double bond between a and b positions
what is another name for an enone
a,b-unsaturated ketone
what reaction is an enone a product of
aldol condensation
T or F: you need heat for aldol condensation
true
if there is no heat in the aldol condensation reaction, what type of reaction is it
a simple aldol reaction
what is the product of the aldol reaction (give both names)
b-hydroxy ketone
aldol
what is the product of the aldol condensation reaction (give both names)
a,b-unsaturated ketone
enone
T or F: aldol reactions may be intramolecular
true
what are the conditions for the intramolecular aldol reaction
must have at least 2 carbonyls on the molecule, and it would need to form a 5 or 6 membered ring
what happens in the crossed aldol reaction (ie what is reacting)
we start with our enolate and react is with an electrophile which is another carbonyl
what is one complication with crossed aldol reactions
the second carbonyl may become an enolate itself, and produce a side product known as an enal (a,b-unsaturated aldehyde)
what is the product of a crossed aldol reaction when the second carbonyl becomes an enolate itself (give both names)
enal or a,b-unsaturated aldehyde
how can we avoid enal production in crossed aldol reactions
we can use a carbonyl that has no alpha hydrogens (because then the molecule cannot be deprotonated to become an enolate)
what is the claisen reaction (name the starting product, what is used, and what is produced)
we start with an ester and react it with a base, producing an ester enolate
what is the product of an ester reacting with base
ester enolate
what is the product when an ester enolate attacks the starting ester
b-keto ester
what types of bases are used in the claisen condensation reaction
OR- rather than OH- so we don’t get side products
T or F: the claisen condensation reaction requires an acid work up (why)
true; it quenches the double enolate formed
why doesnt the claisen reaction produce an aldol or an unsaturated double bond?
OCH3- leaves during the mechanism (super important step)
how do we create a new C-C bond onto a claisen product
react it with RX (alkylation)
what happens when a claisen reaction is heated in acidic conditions
CO2 is released from the b-keto ester = ketone
describe the michael reaction
ketone reacts with base and heat to produce an enone
what is an enone
a,b-unsaturated ketone
T or F: an enone has resonance structures
true
what do the resonance structures of an enone show
the b position is electrophilic (positively charged)
what happens to an enone in the presence of a nucleophile
nucleophile attack on the b carbon, followed by protonated
beta addition occurs
what type of nucleophiles work best in michael reactions
ones that are a resonance stabilized enolate: ie RMgBr or R2CuLi
nucleophiles for michael additions are michael (donors/acceptors)
nuc= michael donor
electrophiles for michael additions are michael (donors/acceptors)
electrophiles = michael acceptors
what type of electrophiles work best for michael reactions
work best when the electrophile is an a,b-unsaturated compound
T or F: all electrophiles for michael reactions are carbonyls
false; they don’t have to be carbonyls, but they must have resonance
T or F: enamines are stabilized enolates (michael donors)
true
since enamines are stabilized enolates (michael donors), what can they do?
they can attack a,b-unsaturated compounds (michael acceptors) to produce an iminium salt
what will we have to do to the iminium salt produced from the enamine in the michael reaction
quench it because it’s a salt (aka hydrolysis)
what happens when an iminium salt is hydrolyzed
it reverts to a ketone
what is stork enamine alkylation
making use of an enamine to perform 1,4-addition
why would we do stork over michael
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)
