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I have been trying to complete this retrosynthesis problem for a few days but can’t figure out how to get from Ester starting compound to a spirocyclic compound. I have tried removing the Ester but can’t figure out what best to replace it with. I have access to any reagents and starting materials as long as the nominated substance is used.

Retrosynthesis

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Step 1 - Form the anion of your starting material ($\ce{NaOEt/EtOH}$ will do this nicely) and react with phenethyl bromide ($\ce{PhCH2CH2Br}$).

Step 2 - Add the product to hot polyphosphoric acid$\ce{^{[1]}}$ to cyclize it to the required product.

Reference

  1. Cyclization of Aryl-Aliphatic Esters with Phosphorus Pentoxide in Phosphoric Acid by Richard C. Gilmore, Journal of the American Chemical Society, 1951, 73 (12), 5879-5880, DOI: 10.1021/ja01156a521
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