Page 942 - Advanced Organic Chemistry Part B - Reactions & Synthesis

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CHAPTER 10
Reactions Involving
Carbocations, Carbenes,
and Radicals as Reactive
Intermediates

complexed with exo,exo-2,3-
Fig. 10.4. Crystal structure of one molecule of Zn(CH 2 I) 2
dimethoxybornane. Reproduced from J. Am. Chem. Soc., 114, 2592 (1992), by permission of the
American Chemical Society.

which is present under most experimental conditions and can have an accelerating
effect. Models were also calculated for the directing and activating effect of allylic
hydroxy groups. Definitive results were not obtained for this case, but an aggregated
structure with the oxygen coordinated to zinc is plausible.
Other reagents have been developed in which one of the zinc ligands is an oxy
anion. Compounds with trifluoroacetate anions are prepared by protonolysis of C H 5
2
or CH I groups on zinc. 179
2

Fig. 10.5. Transition structures for CH 2 transfer from ClCH 2 ZnCl 2 and ClZnCH 2 Cl-ZnCl 2 to ethene
and to coordinated allyl alcohol. Reproduced from J. Am. Chem. Soc., 125, 2341 (2003), by permission
of the American Chemical Society.

179
J. C. Lorenz, J. Long, Z. Yang, S. Xue, Y. Xie, and Y. Shi, J. Org. Chem., 69, 327 (2004).