Acyclic systems double asymmetric

Kitching and co-workers " " developed total syntheses of plakortones C, D, E, and F. Acquisition of plakortone D, the most effective activator of SR-Ca " -pumping ATPase, used stereodefined lactone cores that resulted from asymmetric dihydroxylation of protected homoallylic alcohol 67 (Scheme 15.18). A derived lactone aldehyde was then coupled with an independently generated, sulfone activated side chain unit 68. The 5,6- -double bond, carried through the sequence as a protected, stereodefined diol, was released there by stereospecific sy/j-elimination via an orthoester derivative. Racemic plakortone E was also acquired by using the Pd(II) induced sequence, but in this case, the required, complete acyclic system 69 was assembled first. 

Cobalt is another metal which has been successfully used in asymmetric cyclopropanation. A chirally modified catalytic system for selective cyclopropanation of phenyl-, vinyl- or alkoxy-carbonyl-conjugated terminal double bonds with diazoacetates is formed from cobalt(ll) chloride and (+)-a-camphorquinonc dioxime27,69 71 and similar systems 09. Best optical yields are achieved with styrene and the bulky 2,2-dimethylpropvl diazoacetate which gives 2,2-dimethylpropyl /ra .v-2-phenyl-l-cyclopropanecarboxylate in 88% ee and the as-isomer in 81%ee7n. No cyclopropanation occurs with alkyl-substituted or cyclic alkenes, cyclic or sterically hindered acyclic 1.3-dienes, vinyl ethers and phenylethyne. 

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