Alkenes exocydic

Figure 1.11 provides an example of H NMR monitoring in the Pd-catalyzed cy-doisomerization of dimethyl diallyl malonate, 39 [28]. The kinetic profile reveals a pronounced induction period after which the exocydic alkene 40a is formed predominantly as the kinetic product. A hydropalladation mechanism was proposed on the basis of NMR experiments, and the transient spedes 41, formed by allylpalla-dation of the coordinated diene, could be detected and identified with the help of and labeling. The hydride Pd catalyst, 42, would be generated from 41 by water-promoted P-hydride elimination. The observed induction period is assodated with the formation of the Pd-hydride 42. 

Also in 1982, Knight and Cameron reported Ireland-Claisen rearrangements of lactones possessing both endocyclic and exocydic allyhc alkenes [88]. They also found low dsjtrans selectivity in the rearrangement of 14- and 15-membered ring lactones. 

Brunner and Borschberg [135] employed an Ireland-Claisen rearrangement of a macrocyclic lactone bearing an exocydic alkene in a synthesis of ( )-muscone (Scheme 4.139). Treatment of the lactone with LICA and TESOTf gave a 76 8 ratio of E- and Z[Pg.197]

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