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We've been asked to draw the mechanism for the following pericyclic reaction:

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I know that the tin tetrachloride will act as a Lewis acid and activate the one of the carbonyl groups of the ethyl glyoxylate (I'm not sure which one). I've been trying to see where the cyclic transition state could come from but when I've been drawing the curly arrows I can't seem to get a cyclic transition state (which is required for a pericyclic reaction).

If someone could show me the initial steps of the mechanism then I would be very grateful.

We don't need to consider the stereochemistry for this reaction.

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Although you probably know the answer by now, here is the cyclic transition state. It is an oxy-ene reaction. The Lewis acid lowers the activation energy of the reaction.

enter image description here

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