Tamao—Fleming oxidation conditions

An extensive review has been written which covers in detail the oxidation of the carbon-silicon bond under both Tamao and Fleming oxidation conditions.6 One virtue of the use of these procedures as compared to the related oxidation of organoboron compounds is the fact that the silicon groups can often be carried through several synthetic steps while masking the hydroxyl functionality. 

Another approach to (—)-Lasonolide A has been proposed by Shishido (eq 23). Treatment of a cyclic (bromomethyl)dime-thylsilyl allylic ether under radical-mediated tin hydride conditions afforded the 5-exo-trig cychzation product as a single product. Due to the unstability of this bicyclic compound, the Tamao-Fleming oxidation was carried out in situ giving the 1,3-diol compound in 59% overall yield. This method allowed the formation of contiguous quaternary and tertiary stereogenic centers with total control of the diastereoselectivity. 

Despite the presence of two, relatively weak, N—O bonds ( 53 kcal/mol) (255) nitroso acetals are stable under neutral conditions. Therefore, a number of transformations can be performed on the periphery of the cycloadducts without effecting the nitroso acetal. These include both oxidation of alcohols, dihydroxyla-tion of alkenes (247,248,256), Tamao-Fleming type oxidation (248-250), reductions of ketones and esters (244,257-261), silylation and desilylation (247,257, 260), and activation with a variety of sulfonylating agents (247,248,257-260). 

In the laboratory of F.G. West, the stereoselective silyl-directed [1,2]-Stevens rearrangement of ammonium ylides was investigated as a potential key step toward the enantioselective synthesis of various hydroxylated quinolizidines. The dimethylphenylsilyl group served as a surrogate for one of the hydroxyl groups in the product. The Fleming-Tamao oxidation was performed under Denmark s conditions to avoid oxidation of the tertiary amine to the corresponding A/-oxide, and the desired quinolizidine did was obtained in 81% yield. 

---