[google470]

Hey guys, I am doing a reaction using Zn/AcOH to remove the Cl between the two carbonyl and thus I would like to understand the mechanism. I have drawn a proposal one shown below. Could anyone check it and tell me whether it's correct or not?
Many thanks!!

[google470]

another question is....it seems AcOH didn't play any role in the reaction....  could you tell me why AcOH is used???

[Babcock_Hall]

What kind of chemistry do you associate with acetic acid?

[google470]

What kind of chemistry do you associate with acetic acid?

it provides H+ abstracted by the O- generated after O radical get another e from zinc...

[google470]

What kind of chemistry do you associate with acetic acid?

Thanks!!
I redraw the mechanism, protonation of the C=O by AcOH should be the first step followed by SET..

It is correct?

[Babcock_Hall]

What kind of chemistry do you associate with acetic acid?

it provides H+ abstracted by the O- generated after O radical get another e from zinc...

This seems reasonable.

[zarhym]

I don't think it's a radical mechanism. There is no radical initiator here.

[Babcock_Hall]

I don't think it's a radical mechanism. There is no radical initiator here.

Do you think that Zn could provide an electron?

[zarhym]

I don't think it's a radical mechanism. There is no radical initiator here.

Do you think that Zn could provide an electron?

Well, if it's not SN2,  how would you still have the chiral center the same after the reaction?

[zarhym]

I don't think it's a radical mechanism. There is no radical initiator here.

Do you think that Zn could provide an electron?

I mean I would agree with you if the product is a racemic mixture.

[zarhym]

Alright, I attached the mechanism I in my mind. The only reason I think it's not a radical mechanism is because the chiral center stays the same.
I also provided a reference in the attachment below, which should be strong enough to support my idea. 

First of all, I believe the AcOH is simply used to activate Zinc powders so that zinc oxide coating could be removed. It may also help zinc dissolved in organic phase.
Then, metallic zinc insertion happens since the zinc is activated by acid. After the step i), the zinc complex is the intermediate which goes into next step.

After tBuOK added, it not only removes the acidic hydrogen on MVK but also removes zinc-halogen moiety in order to create another carbanion (see attachment below).
And eventually the ring closes.

The key difference is this.
The chiral carbon in mechanism you proposed is sp2 hybridized in the transition state, which will lead to recemic mixture eventually.
The chiral carbon in my mechanism is all-the-way sp3 hybridized, this will prevent recemic mixture.