Difficult mechanism problemhelp

[shiznites]

ORGANIC CHEMISTRY II

Homework Statement

I spent hours trying to figure out how to do this mechanism but I always get stuck. Its tricky and will make you think.. think you can figure it out?

Homework Equations

Figure out the mechanism just using acid (H+)

The Attempt at a Solution

I started out by reducing the epoxide by protinating and was left with a -OH group on each carbon that made up the epoxide. Using one of those -OH groups I attack the carbonyl on the opposite side (using the -OH group as a nucleophile).

Basically I don't know where to go from there or if that's even a correct start. I sat here for awhile staring at my 3D model and came up nowhere. I know that somewhere down the line there will be dehydration somewhere.

Your help is greatly appreciated =]

 

[chemisttree]

Look at the rightmost ring in the product. Assume that the carbonyl carbon is preserved in the reaction. Count the carbons starting with carbonyl then methylene then the two bridged carbons and finally the oxygen. How many units in the ring? How many carbons? Assume that the bridged carbon to oxygen bond in the ring is preserved in your mechanism. Now you know what part of the molecule is unchanged in the mechanism. Start your mechanism by protonating the epoxide as you suggested and then break one of the C-O bonds. Remember that one of those C-O bonds winds up in the product (so don't break that one!) and the carbon attached to it becomes a bridged carbon.

 

[shiznites]

I figured it out.

Hydrolysis to the epoxide which breaks it open. Then Fischer esterification which forms the ester bridge. Upon the completion of Fischer the adjacent C-C bond breaks to reform the carbonyl from the intermediate. This leaves a cation. Dehydrate and bam.