Fetizon reagent

Selective oxidation. The diol 1 is oxidized to the lactone 3 (cinnamolide) in 55% yield by Collins reagent. The same oxidation with AgiCOi/Celite (Fetizon reagent) is essentially quantitative. The cheaper barium manganate is equally effective, and has the advantage that the intermediate lactol 2 can also be obtained if desired. 

Particularly satisfying was the ease with which 157 was homologated to 158 (92%). Reduction of the ketone carbonyl in a chemoselective manner was not possible because of the steric protection it benefits from. This potential complication was skirted when it was found that the hydroxy lactol produced by diisobutylaluminum hydride reduction responded to the Fetizon reagent only at the five-membered site to deliver 159. With the stereochemistry of 159 securely established by NOE analysis, no obstacles were encountered during acetylation and the subsequent completion of sidechain construction. 

Kinetic resolution of another allylic alcohol in the Sharpless epoxidation was also employed in the synthesis of (Jl)-lO and fully oxygenated AB building block 35 (Scheme 6) [47]. Epoxidation of alcohol 34 [48] followed by LAH reduction and then oxidation with the Fetizon reagent [41,49] furnished hydroxyketone (Jl)-lO. Ketahzation of the carbonyl group and subsequent stereoselective benzyUc hydroxylation, using iodosobenzene in the presence of [ 5,10,15,20-tetrakis(pentafluorophenyl)-2 lH,23H-porphine ] iron(lll) chlo-... 

Likewise 5a-androstane-3/S,17/S-diol is oxidized to 5 -androstane-3 8-ol-17-one (68 yield). The selectivity in these oxidations is greater than that obtained with the more expensive Fetizon reagent. 

Application of the Fetizon reagent (AgCOa-celite) to monomethyl aldoses has been proposed as a means of assigning the position of the ether group. The reaction product is first reduced to the alditol, trimethylsilylated, and examined... 

Silver oxide adsorbed on to celite (Fetizon reagent) has been used to effect the oxidation of aldoses from the C-1 position in a series of degradation steps which cease when the 2-0-substituted aldose is formed. The method has been applied to the determination of the substituent position in mono-O-methyl-aldoses. 

Radical oxidative cycloaddition of 4-hydroxycoumarins to alkenes has also emerged as a powerful tool for the rapid construction of dihydrofuro[3,2-c] coumarins [83-87]. The fact that 4-hydroxycoumarins behave as 1,3-dicarbonyI systems allows the easy generation of a,a-dicarbonyl radicals, which can be readily added to the C=C bond of the alkene. First examples of this reaction were described in 1998 by Lee and coworkers employing Ag2C03/celite (Fetizon reagent) as promoter [83]. A variety of olefins such as styrenes, dienes, vinyl ethers. 

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