Claisen - 6-3-2011 at 02:33
(A)
The oxygen of the ether group gets protonated in the first step, followed by bond cleavage to form vinyl carbocation and alcohol.
Nucleophilic attack of water on the vinyl cc forms vinyl alchol.
So the options to be matched in the Right column is (4)
But the answer includes (5) too and I have no idea of the formation of aldehyde in any step.
Any hint would be sufficient I guess.
DJF90 - 6-3-2011 at 10:03
First step is hydrolysis of alkyl enol ether (most likey place you will find an example of this is as one of the steps after birch reduction of
anisole in the preparation of cyclohexenone(s)). Second step is hydrolysis of the alkyne via oxymercuration, yielding an enol as the "first product"
which will tautomerise to give you a ketone. The third reaction is likely an intramolecular cyclisation of the enolate on the terminal chlorine (A
5-exo-tet cyclisation - see Baldwin's rules). As for part 4 - I don't really understand what the question is asking, but a gem-halohydrin is an
unstable "product" and I suspect it would fall apart to give the acetophenone and HBr (although these products could react again to give
a-bromoacetophenone).
Claisen - 6-3-2011 at 13:41
I asked only for part (A) 
Any way thanks for your time 
I still have a problem in (A),
Is my explanation for the steps in OP not correct?
DJF90 - 6-3-2011 at 13:53
The lone pair on the enol ether can push in and protation occurs on the b-carbon of the of the vinyl group. The mechanism from then on is identical to
that from acetal hydrolysis.
The route you propose, whilst protonation on oxygen would be a good first guess, involves the formation of a vinyl carbocation, something that isnt
particularly favourable (c.f. primary carbocation). Vinyl alcohol wouldnt exist as such, seeing as it readily and likely completely tautomerises to
acetaldehyde. The enol tautomer is usually more favourable when additional conjugation is made possible, e.g. you might expect ethyl acetoacetate to
exist partly as the enol form, due to conjugation of the enol C=C double bond with the ester group.
Claisen - 6-3-2011 at 14:13
Thankyou very much!!