Acetonide function

Regioselective protection of the pentaol 230 with bis-trichloromethyl carbonate and subsequent acetic anhydride treatment affords the C-10 acetoxy C-l, C-2 carbonate compound 231 in good yield. Deprotection of the acetonide function and regioselective silylation of the C-7 hydroxyl group, followed by... 

Compounds 80 and 93 were reisolated by Sawa and his cowoikers from C. cordata along with a new biaryl type macrocyclic diarylheptanoid (84) containing an unusual diol acetonide function. 

The reaction tolerates a wide range of functional groups, including base-sensitive (ester) and acid-sensitive (acetonide) functionality, as shown in the following exam-ples. ... 

In addition to sulfur ylides, examples are known of cyclopropanations using other ylides containing group V or group VI elements. Among these, triphenylphosphonium ylides have most frequently been studied. Some examples are collected in Table 19. The products obtained in entries 1-3 and 10 of Table 19 are suitable precursors for chrysanthemic acid. An enantioselec-tive synthesis of cyclopropanes was achieved by using electron-deficient alkenes substituted with an optically pure oxazolidine or acetonide function. When the alkene is stabilized by a ketone or nitro function instead of an ester function, the yield dropped considerably. 

Perhaps classical for the protection of 1,2- and 1,3-cis-diols is the isopropyl-idene (acetonide) function. This acid labile ketal may be formed by reaction of a ribonucleoside with acetone in the presence of an acid (HCl, p-toluene-sulfonic, H2SO4) and water scavenger (2,2-dimethoxypropane, ethyl orthoformate). Other similar protecting groups include the benzylidene and cyclohexylidene functions. 

Unique chemistry is associated with the cyclopentenone all five carbon atoms can be functionalized, and the endo-methyl groups of the acetonide assure clean stereoselective addition of the alkenylcopper reagent from the convex side. The use of the acetonide group to control enolate regioselectivity and to mask alcohols should be generally applicable. 

CH2(OMe)2, CH2 = CHCH2SiMe3, MeaSiOTf, P2O5, 93-99% yield." This method was used to protect the 2 -OH of ribonucleosides and deoxyribo-nucleosides as well as the hydroxyl groups of several other carbohydrates bearing functionality such as esters, amides, and acetonides. 

Isotope labeling by derivative formation with deuterated reagents is useful for the preparation of analogs such as dg-acetonides, da-acetates, da-methyl ethers, dg-methyl esters, etc. The required reagents are either commercially available or can be easily prepared. (The preparation of da-methyl iodide is described in section IX-F. Various procedures are reported in the literature for the preparation of dg-acetone, da-diazometh-ane57.i63.i73 and da-acetyl chloride. ) These reactions can be carried out under the usual conditions and they need no further discussion. A convenient procedure has been reported for the da-methylation of sterically hindered or hydrogen bonded phenolic hydroxyl functions by using da-methyl iodide and sodium hydroxide in dimethyl sulfoxide solution. This procedure should be equally applicable to the preparation of estradiol da-methyl ether derivatives. 

During attempted acetonide formation of an amino alcohol derivative, smooth tosyl cleavage was observed. The reaction is general for those cases having a carboxyl group, as in the following example, but fails for simple amino alcohol derivatives that lack this functionality. ... 

Intermediate 8, the projected electrophile in a coupling reaction with intermediate 7, could conceivably be derived from iodolactone 16. In the synthetic direction, cleavage of the acetonide protecting group in 16 with concomitant intramolecular etherification could result in the formation of the functionalized tetrahydrofuran ring of... 

The completion of the synthesis of key intermediate 2 requires only a straightforward sequence of functional group manipulations. In the presence of acetone, cupric sulfate, and camphorsulfonic acid (CSA), the lactol and secondary hydroxyl groups in 10 are simultaneously protected as an acetonide (see intermediate 9). The overall yield of 9 is 55 % from 13. Cleavage of the benzyl ether in 9 with lithium metal in liquid ammonia furnishes a diol (98% yield) which is subsequently converted to selenide 20 according to Grie-co s procedure22 (see Scheme 6a). Oxidation of the selenium atom... 

Both the regiochemistry and stereochemistry of Wacker oxidation can be influenced by substituents that engage in chelation with Pd. Whereas a single y-alkoxy function leads to a mixture of aldehyde and ketone, more highly oxygenated systems such as the acetonide or carbonate of the diol 1 lead to dominant aldehyde formation.107 The diol itself gives only ketone, which perhaps indicates that steric factors are also important. 

Treatment of the elimination product 107 with triethylamine resulted in smooth isomerization of the olefin, to afford the a,p-unsaturated ketone 108. Ally lie oxidation of 108 then generated the secondary alcohol 109 in 72 % yield. The acetonide and silyl ether functions of 109 were cleaved in one reaction to afford a tetraol intermediate that was regioselectively acylated at the secondary alcohol functions, to provide the triacetate 110 in high yield (89 %). Hydrogenolysis of the benzyl ether... 

Our retrosynthesis of (—)-kinamycin F (6) is shown in Scheme 3.20 [45]. It was envisioned that (—)-kinamycin F (6) could be prepared from the protected diazofluorene 114 by conversion of the ketone function of 114 to a trans-], 2-diol, followed by deprotection of the acetonide and methoxymethyl ether protecting groups. The diazofluorene 114 was envisioned to arise from diazo transfer to the hydroxyfulvene 115. The cyclopentadiene substructure of 115 was deconstructed by a two-step annulation sequence, to provide the bromoquinone 116 and the p-trimethylsilylmethyl unsaturated ketone 117. The latter two intermediates were prepared from juglone (118) and the silyl ether 119, respectively. 

The diol function of 130 was protected as its acetonide 131 (88 %). Next, the enone function was installed by a-selenation of the enoxysilane, followed by peroxide oxidation and elimination (57 % over two steps). Finally, the unsaturated ketone 132 was homologated by 1,4-addition of trimethylsilylmethyl magnesium chloride, trapping with chlorotrimethylsilane, and reoxidation, to afford the target 117 (88 %). 

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