Page 219 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

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SECTION 2.5
Enantioselective
Reactions

(a) (b)

(c) (d)

(e)
Fig. 2.21. Successive models of the transition structures for Sharpless epoxidation: (a) the
hexacoordinate Ti core with hydroxide and hydroperoxide ligand and a coordinated alkene;
(b) Ti with methylhydroperoxide, allyl alcohol, and ethanediol as ligands; (c) monomeric
catalytic center incorporating t-butylhydroperoxide as oxidant; (d) monomeric catalytic center
with formyl groups added; (e) representation of the active dimeric catalyst. Reproduced from
J. Am. Chem. Soc., 117, 11327 (1995), by permission of the American Chemical Society.