7d

Question 1

whats an enantioselective reaction

Answer 1

a reaction where 2 enentiomers are made but one is made faster // at a greater ratio than the other

Question 2

how are enantioselective reactions a thing??? like how is one enantiomer made more than the other if enantiomers are known for having the same reactivity and therefore the same ROR and ratio

Answer 2

there has to be smt diastereoisomeric about it

and this is its transition state!!!!

Question 3

what does epoxidation allow

Answer 3

epoxidation allows us to attack the alkene from the back or the front

u have 2 options!!! so youd get enantiomers, one wedged and one dashed

Question 4

whats cool about diastereoisomers again

Answer 4

they have diff energies and therefore diff ROR and therefore are made in diff ratios

Question 5

when we have achiral sm and form smt chiral,, what does that mean

Answer 5

we def had smt diasteromeric in between that made it chiral

Question 6

okay describe the energy diagram that makes a enantioselective process

Answer 6

u have ur SM which are achiral at the bottom

then u have the ts which is a diastereomeric ts

thenu. have the enantiomeric products

the 2 lines arent overlapping bc they have diff enenrgies

due to the diastereomeric ts

meaning one enantiomeric product is made faster and more is made .

Question 7

okay when we go from achiral to chiral ,, what do we use to do this

Answer 7

we use either a chiral catalyst,, in reactions that cannot undergo without a catalyst

or we use a chiral oxidising agent !! either an S or R one.

Question 8

what does a chiral catalyst do to the reaction

Answer 8

it adds chirality

it adds an O to the substrate

Question 9

okay when we have an alkene with a CH2 and then an OH after this,, and we want to perform an epoxidation reaction using an S-catalyst,, what ts and products do we get

Answer 9

we get the dashed epoxide with an S catalyst attached to the O : this will be SS

then u have the wedged epoxide with the S catalyst attached to the O. this will give us SR

and these are diastereoisomers

aka we get diastereosiomers as products

Question 10

okay describe the sharpless asymmetric epoxidation

Answer 10

u have ur alkene with CH2 and OH after this!!!

then u need ur
Ti(Oi-Pr)4
t-BuOOH
i-PrO2C- OH wedge - OH wedge - CO2i-Pr (this is the chiral bit and its S config)

the Ti from the Ti(Oi-Pr)4 coordinates to the O of the OH of our starting material. then it also corrdinates to the O from t-BuOOH.

this arrannges the moecule in a way that adds the O from t-BuOOH on one side of the allylic alkene

Question 11

when we say the alkene with the CH2 and the OH at the end, what is this acc called

Answer 11

an alyllic alcohol!!!

Question 12

whats an allylic alcohol

Answer 12

when the OH group is bonded to the C adjacent to the double bond.

Question 13

whats chemoselective mean

Answer 13

when a reagent prefers to react with one fg over the other fg’s.

Question 14

what does allylic mean

Answer 14

the carbon adjacent to the double bond

Question 15

okay we dont need to know the jacobsen epoxidation but expoain what happens

Answer 15

manganese complex has a chiral ligand ( and we only have a single enantiomer of this - aka only its S or R)

this means that its able to give asymmetry and stereoselectivity!!

we get an epoxidation where both things are wedged from an alkene. RS

Question 16

describe sharpless asymmetric dehydroxylation

Answer 16

its when an alkene gets 2 OH’s added to it

both wedged!!!!

Question 17

what chiral ligand do we use for sharpless asymmetric dihydroxylation

Answer 17

we use (DHQD)2 PHAL
so get both wedged

and we use (DHQ)2 PHAL as the enantiomer of the chiral ligand to get both dashed

this is bc the chiral complexes arent rlly enantiomers,, but they react as if they were. they function as enantiomers so we just use them as they were.

think that one of them already have D in their name so they need to have wedged products

and the one that doesnt have a d in its name needs dashed products

Question 18

what previous way do we know we can hydrogenate smt

Answer 18

we can do this by using the metal surface and then the alkene approaches it and u have symmetric hydrogenation

Question 19

what happens during asymmetric hydrogenation

Answer 19

we have an achiral ligand and H is added to both faces of the double bond to form a racemic mixture.

when we have a chiral ligand (but only one enantiomer of it) it only attacks from one side, so we get one product formed more than the other.

Question 20

in the catalyst /// ligand used in asymmetric hydrogenation,, what atom is chiral

Answer 20

the P!!!

bc it has 3 diff groups and a lone pair!

so P is the chiral one.

Question 21

are alkenes the only thing that can be hydrogenated,, also ehat is hydrogenation btw

Answer 21

hydrogenation is when u add H to a double bond

alkenes can by hydrogenated but so can carbonylsssss

Question 22

whenu hydrogenate a carbonyl what do u get

Answer 22

u get an alcohol.

Question 23

what does using a chiral ligand on an achiral molecule do when we hydrogenate smt

Answer 23

the chirality of the ligand makes one enantiomer of the product favoured over the other

so we get an enantioselective reaction!!! where the TS is diastereomeric,, aka diff in energy,, allowing diff ratios of enantiomers to be made.

Question 24

if u have a cyclohexane with MgBr,, aka a gringard reagent attached to it,, and u react it with an aldehyde what happens

Answer 24

the aldehyde takes the place of the MgBr

and u have an alochol bc the aldehyde will be hydrogenated!!!

Question 25

what reacts the same as gringard reagents

Answer 25

dialkyl zinc compounds!!! aka R2-Zn the zinc compounds are slightly less reactive tho!!!

Question 26

due to the dialkyl zinc compounds being less reactive than gringard agents,, to react them with an aldehyde,, what do we need to do

Answer 26

we need a catalysttttt

Question 27

what type of catalyst do we need in the dialkyl zinc aldehyde reaction

Answer 27

we need amino alcohol catalyst aka like smt like DAIB

Question 28

describe DAIB

Answer 28

catalyst needed for dialkyl zinc to react with aldehydes its like a bent rectangle with NMe2 top right,, OH bottom right and we have a hut with 2 methyl groups joining the 2 middle carbons and u then have a methyl coming from one of the middle carbonssss of the framework

Question 29

okay when u have a MgBr and an aldehyde what is the product

Answer 29

the alldehyde attaches to where MgBr was,, and an alochol forms but this will now be a chiral centre meaning u can have dahsed or wedged . normally a racemic mix is madeeeeeee. aka 50:50 ratio of both enantiomers

Question 30

okay so if we want to make one enantiomer over the other when we have a gringard and an aldehyde,, what do we normally think to do

Answer 30

we normally think of making the gringard asymmetric ,, aka making it chiral but we cant do this bc the gringard is too reactive

Question 31

whats a downside to aldehyde and dialkyl zinc reactions

Answer 31

they occur so so slowly like they basically dont react unless u have a catalyst with them. (aka an amino alcohol ligand) which speeds up the reaction. we just need to make sure the catalyst is asymmetric aka chiral.

Question 32

think of DAIB,, the folded rectangle aka cyclohexane with NMe2 top right, OH bottom right,, Me in the centre and the bridge over the central carbons with the 2 Me sticking out ,, how many stereocentres does it have and what do we call them to simplify things

Answer 32

it has 4 stereogenic centres but they all associate with eachother so theyre all S or all R so we just say DAIB has 2 forms,, S or R. and we say theyre basically in a racemic mix bc the mix is 55:45 which is basically racemic.

Question 33

when u have DAIB and a dialkylzinc ,, what happens

Answer 33

a dimer forms (Me2Zn with DAIB) and the dimer and monomeric form are in equilibrium!!!

Question 34

the dimer is made up of a monomer,, and if the monomer is S or R,, the dimer can be what

Answer 34

it can be SS RR SR or RS righttt !! bc if the dimer is made up of 2 monomers,, and the monomer is either R or S,, u have those options available!! makes sense girl youve got this.

Question 35

what dimer form is super stable and doesnt do anything

Answer 35

the RS form!!!! its super stable and doesnt do anythingggg

Question 36

okay so lets say u have an enantiomer mixx of 45:55 and u have RR + SS <--> 2S + 2R <--> 2RS and the 2RS are super stable. what do the 45 and 55 do

Answer 36

the 45 enantiomer,, lets say S,, takes 45 of the the R enantiomer to form RS meaning no SS can be formed bc all the S is used up and only a few RR can be made,, bc obvs majority of it went to making RS/SR. so the minor enantiomer uses the major enantiomer. and bc RS is catalytically inactive,, and theres no SS,, we just have RR dimer!! so we produce one type of enantiomer product bc of this !!!!!

Question 37

what does the enantiomeric excess thing mean

Answer 37

if u have an e.e of 0 it means u have a racemic mixture if u have an ee of 100 it means one enantiomer is formed and the other one isnt.

Question 38

how do we do amplification of stereochemistry!!!

Answer 38

we have aldehyde + R2Zn which give us a racemic mix but one enantiomer is slightly slightly more abundant than the other one. and this enantiomer is used as a catalyst or smt like that ,, and its used 6 times in diff reactions and each time its ee slowly increases the autocatalytic reaction can lead to a larger enantiomeric excess of one of the enantiomerssss!!