Let's talk about organocuprates or Gilman reagents.
So Gilman reagents are less basic than Gilma- than organomagnesium or Grignard reagents,
organolithium so they're known as a coupling reagent because they couple two carbon groups
together, alright.
And they're not going to react in the, with acidic groups, like alcohols and amines
and so we're going to be able to have these groups on our reagent as we're doing the reaction
and without worry about an acid-base reaction occurring, and essentially we're gonna
replace a halide with a new alkyl group.
The other good thing about these is we're gonna see coming up is that they are unreactive
with carbonyls, but Grignard do react with carbonyls and the organolithiums do as well,
and so that would be something we couldn't couple in the presence of a ketone, for example.
We're gonna be able to do that in the present with an organocuprate.
So let's have a look at, at our procedure here.
So as with any organometallic, the first thing we've got to do is make the reagent and so
we do that with an organolithium, like butyllithium here.
And then copper iodide salt, okay.
So we add those two together, two equivalents of the organolithium and we're gonna stick
two of those, butyl anion groups onto the copper iodide substrate to form the cuprate
and so our reagent here that we just made is this species here so we've got a butylcuprate
right here.
Now, the next thing we want to do is use it and so it's best if we make, using a primary
organolithium, we've talked about how to make those already with an alkyl halide and lithium
in excess in a hexane solvent, so that primary group there couples quite nicely onto the
Gilman reagent.
There are ways of doing secondary, but we're not going to look at those because there are
many stipulations that go along with it.
However, if we stick with a primary Gilman reagent like we have here, so this is a primary
group on this Gilman reagent, it's best if we don't, if we avoid secondary or tertiary
alkyl groups, but there are methods that generally work with primary Gilman's that can achieve
these so if the book's not going to show many of these, but if you want to use those go
right ahead, could be because there are ways of getting it done with, with different catalysts
and formulations of higher order cuprates.
So anyway, what does that mean?
Well, it means let's use the reagents, so all we're going to do is take an alkyl halide,
best if a primary, so we'll say how about this ethylbromide here or 1-bromoethane and
so we can take our group here from the cuprate that I'll mark in read like we originally
did.
So this is our carb-, our four carbons from the cuprate, only one of them participates
and then we get the two carbons of the ethylbromide as well.
So we end up with 1, 2, 3, 4, 5, 6 together.
And again that's a primary bromide so best with best we're good to go, but notice I didn't
say you couldn't use other groups here.
We can use alkyl groups that are primary, but we can also use vinyl groups or aryl groups.
and any group, but those secondary or tertiary alkyl, so it's pretty versatile as we'll see
from our practice here.
So other than primary alkyl to primary alkyl, what else can we do?
Well we could use this, we could create this vinylcuprate from a vinyllithium - two equivalents
mixed together, two vinyl groups to form the cuprate, not worried about the lithium iodide
by-product here, but we can also couple aryl halides.
So we'd be exchanging this alkyl or this group, carbon group for that bromide and exchanging
the two.
And so what we get out of this coupling, be the aryl compound, replace the bromine with
the vinyl group, eliminate some copper lithium bromide by-product there and we have a wasted
equivalent, a vinyl that doesn't react, but again the by-products aren't that important
here.
But we can couple different functionalities than we can with the Grignard reagent.
We could make a Grignard reagent from a vinyl group, but we couldn't couple it to an aryl
group like we see here, at least would not advance catalysts.
So that being said, the Gilman is preferred here due to the enhanced functionality.
Well what else can we do?
Well if we made the same reagent here, so let's keep with this vinyl cuprate.
When we go to use it, what if we have a halide that has an acidic group present?
Okay, so here with the coupling reaction that OH is not affected, we're not very basic because
copper to carbons is not a very polar bond and so we can take that bromine off, it was
here - one, two, three carbons - and now we just put that vinyl group on one, two more
carbons in place of the bromide.
Okay, if we were to do this same reaction with a Grignard reagent, cuprate versus an
organomagnesium, vinylmagnesium bromide, same setup here with the alkyl halide.
Instead of getting our desired substitution, we would end up with a deprotonation reaction
that would bubble off ethylene gas and it would create a good nucleophile, strong base
in the presence of a primary halide and you would end up getting an SN2 reaction to form
an ether, the very similar reaction of a Williamson Ether.
So oxygen, carbon, carbon, carbon, that's four we would end up with a cyclic ether as
our final product if we'd use the Grignard reaction, so not exactly what we were expecting.
The Gilman allow us to couple that vinyl group on without interacting with the by-product
or with the acidic protons.