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any idea, guys?
I think inversion is probably because Sn2 happened, but not sure the retention. we can't do Sn1 cuz we don't want racemization
this way you transform oxygen into a better leaving group by using tosyl chloride, it doesnt change the configuration at the chiral carbon. then you use a sulfur analog which reacts in an SN2 fashion, causing inversion of stereochemistry leading to your product. "Sulfur analogs of alcohols are called thiols or mercaptans, and ether analogs are called sulfides. The chemical behavior of thiols and sulfides contrasts with that of alcohols and ethers in some important ways. Since hydrogen sulfide (H2S) is a much stronger acid than water (by more than ten million fold), we expect, and find, thiols to be stronger acids than equivalent alcohols and phenols. Thiolate conjugate bases are easily formed, and have proven to be excellent nucleophiles in SN2 reactions of alkyl halides and tosylates. R–S(–) Na(+) + (CH3)2CH–Br (CH3)2CH–S–R + Na(+) Br(–)"
I kind of thought about the same thing
Yep, thats TsCL, I know that
Thats your tosylate, this is an excellent way to transform oxygen into a better leaving group
How about the retention part?
to my knowledge it does not change or cause inversion of a chiral center so I think it's retained.
then after that, when you see an inversion of stereochemistry for this problem, i WAS THINKING an SN2 reaction.
Well, attach OTs dies not, but the Sn2 with Set- does right?
SO We have to figure out something other than a SN2 from the second reaction
Well after we make the OH a better leaving group we need to get it off and the configuration has to be inverted, SN2 was what I was thinking. |dw:1449439971615:dw|
If we do an SN1, we would get both enantiomers, and that's not what we want, so I am out of tricks now
@caozeyuan I agree another thing to do is to pay attention to what the configuration of the products is along with what groups were added. remember well we could do SN1 but we would get both enantiomers. in this product we have one enantiomer predominating so we need to figure out how to get that. that's why I used a sulfur analog because they are known to perform sn2 like reactions. we have a secondary substrate.
Yes, but this time we want to preserve the sterochemistry, we don't want inversion anymore, I really cannot think of any reaction and add sulfides and give retention
I have another idea
we can do another reaction and use instead SOCL2 to get the other enantiomer |dw:1449440638921:dw|
ok, so step one turns OH into Cl, right? and step 2 is replace Cl with Set, right? So why is this case retention
@caozeyuan if you use SOCL2 it will cause an inversion of your starting material so and take a look at this
I See!, two inversion is retention! Cleaver!
Now I understand!
so that's how you would get both of these transformations
Yes! so it depends on what reagent you use. if you want to change the sterochemistry of one of the chiral centers you can use SOCL2 to do that.
look at the final products too, those will give you clues as to what to do. also we could have used PBR3 it acts in the same way chemically as SOCL2
Great! tank you so much!!
no problem take care