The following is an example of a reaction sequence developed by Derin C. D'Amico and Michael E. Jung (UCLA) that results in enantiospecific formation of two new chirality centers and a carbon-carbon bond. The sequence includes a Horner-Wadsworth-Emmons reaction (Section 16.10B), a Sharpless asymmetric epoxidation (Section 11.13), and a novel rearrangement that ultimately leads to the product. Propose a mechanism for rearrangement of the epoxy alcohol under the conditions shown to form the aldol product.

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(1) CH CHCO CH OH O(OCH ,, NaH (2) DIBAL-H CH t-BuOOH, disopropyl tartrate TBSO Ο TBSOT (t-butyldimethylsilyl triflate), 1.3 equiv он N.N-ethyldiisopropylamine, 1.35 equiv. molecular sieves, -42 C CH3 CH 94% (95% enantiomeric excess)