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I'm solving past problems from a 2014 Organic Chemistry II course (from a publicly available Harvard summer school Canvas page), when I came across this question:

enter image description here

The answer (which is the reactant) looks like this:

enter image description here

Now I understand how the alkyne would turn into an alkene, but I don't get how a furan would form from what looks like an oxymercuration-demercuration reaction. Any help would be much apprecited.

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Observe that there is no nucleophile give in the mercuration step and recall that the three-membered mercury ring intermediate is very reactive. Hence, this is suggestive that the oxygen would attack the intermediate with its lone pair on the more substituted position as follows:

enter image description here

Edit: Oops! Missed a carbon on the last step as correctly pointed out by @Waylander. I have updated the answer with a new image that corrects the mistake.


For reference see Addition reactions of Alkene's in David Kleins organic chemistry (around page-410 ) and for a quick reference see wiki

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  • $\begingroup$ You are missing a carbon in the final structure - otherwise this looks correct $\endgroup$
    – Waylander
    Jan 4, 2021 at 10:06

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