hey guys so for this practice problem we have this starting material we've got
this alkyne and we are going to subject this to a series of three reaction
conditions and so we want to take a look at these see if we can think of what
kind of chemistry might be happening and we want to draw the product of this
sequence of reactions so give it a shot.
so let's take a look at this for the first reaction immediately we might be a
little bit confused at first because we are seeing clearly a grignard reagent
right we know that we are going to be reacting this substrate with a grignard
reagent but the thing is we know that usually grignard reagents are going to
attack carbonyl containing compounds and we don't see any carbonyl containing
compounds here but we know that this is actually right this is a pretty
strongly partial minus, it's a pretty strongly
has a pretty strong partial negative charge on that carbon that's why it's
able to act as a nucleophile and we know that nucleophiles can either coordinate
to a substrate or they can do an acid-base reaction if there's a
sufficiently acidic proton that's why we never run grignard in aqueous conditions
because it'll just react with water and then that'll ruin your grignard reagent
and so that's no good now we don't have any any protons on here that are as
acidic as waters protons but we do have we do have this alkynyl proton and as
it happens that alkynyl proton actually is acidic enough to do acid-base with
this grignard reagent so even though this isn't the typical thing that you
see a grignard reagent doing this is a sort of critical thinking that we have
to be able to employ we have to say all right there's a grignard
there's no carbonyl what else can it do I know it can do acid-base and clearly
the most acidic proton on there is that alkynyl proton so this is just a
little bit of an unorthodox way of doing it but we are going to prepare the
acetylide anion right so this has lost that proton we've got a formal negative
charge on that sp carbon right there and so that's the first one now what well
we've got this epoxide right so we've got the epoxide and we know from
when we looked at epoxides we know that they are susceptible to
nucleophilic attack right it's a three membered ring and if we have a good
nucleophile we're gonna be able to pop that ring open and we do in fact have a
good nucleophile, the acetylide anion as we've said is a good nucleophile because
it's sort of bullet shaped it's it's linear so we have a formal negative
charge on this carbon and and there's not a lot of steric hindrance so this is
gonna be able to go ahead and attack and pop that open so we have let's be very
clear about our carbons we have one and then we have our triple bond and then
this carbon is now bound to these two carbons so we have to go one two right
we are tacking on two carbons right there that is these two right there so
from this carbon we must have two new ones and then that last one is still
connected - OH - so we have to draw that there so that's what happens these two
carbons used to belong to this epoxide there and now lastly we're just going to
do aqueous acidic workup we're just going to protonate this oxyanion and we
are going to get our product
and we will have this alcohol so this is an interesting sequence here we did
something unorthodox with the grignard reagent to prepare the acetylide ion we
use the acetylide ion to attack this epoxide pop it open and then simply
protonated to get this hydroxyl group on there so that is going to be the product
of this sequence of reactions.