Asymmetric dihydroxylation, 74, release

The new development is that electrochemical oxidation of ferrocyanide to ferricyanide can be coupled with asymmetric dihydroxylation to give a very efficient electrocatalytic process. The electrons necessary to the reoxidation of Fe(II) are provided by water that is reduced to OH and H2. Hydrogen gas, released at the cathode, is the only by-product of this process. This electrochemical device uses iron in catalytic amounts ( 0.15 equivalents per equivalent of olefin). 

AD) and the application of a catch-and-release procedure using a supported boronic acid to effect in-line purification of the diol 20 (Scheme 5). The enantiomer of 20 could readily be obtained through the use of AD-mix-p in the Sharpless asymmetric dihydroxylation reaction. The two alcohol groups of the diol could subsequently be differentiated using an enzymatic selective protection. 

Use of the immobilized iridium double-bond isomerizing catalyst (70) developed for the carpanone synthesis again worked well to convert commercially available 73 to the conjugated product (74). This was then methylated in the presence of PS-BEMP (7), a reaction that proceeds in almost quantitative yield. Next, an asymmetric dihydroxylation was performed according to methods developed by Sharpless. However, instead of using a conventional workup procedure for the vicinal diol (75), a new catch-and-release protocol was developed. This made use of the immobilized boronic acid (76) to trap the chiral diol... 

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. 

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