Triacetate, acid cleavage

Amino Acid and Carboxylato Complexes. Rate data for the formation kf) and dissociation (fcj of [Cr(X)Y] " ions from the reactions of [Cr(Y)(OH2)] "" " ions from the reactions of [Cr(Y)(OH2)] " ions H4Y = edta, H3Y = A-(hydroxyethyl)ethylenediamine-A, A, 7V -triacetic acid (hed-tra), ethylenediamine-N,A, A -triacetic acid (edtra), and A -methylethyl-enediamine-A,A, N -triacetic acid (medtra) with anions X" (NOi",Nf, NCS") are collected in Table 5.11. The accelerated rates of anation and aquation are ascribed to transient coordination of the pendant groups of ligands Y"". Nitrite ion probably reacts without Cr-0 bond fission in the case of [Cr(hedtra)(H20)]. However, for [Cr(medtra)(H20)] nitrosation proceeds via parallel reactions, one with and one without Cr-0 bond cleavage. 

The wrong stereochemistry at C(2) was corrected at this stage by selective oxidative cleavage of the O-benzylether followed by inverting the resulting P-alcoho 41, by Mitsunobu reaction to the corresponding a-benzoate 42. Sequential hydrolysis of 42, first by basic methanol, and then with acid provided a triol which was converted into the corresponding triacetate 43. Exposure of 43 to trifluoroacetic acid liberated tri-O-acetyl-7-deoxynarciclasine, the methanolysis of which furnished (+)-7-deoxynarciclasine (31). 

IOB alone can oxidize some alcohols, but catalysed oxidations are much more efficient. Thus, in the presence of RuCl2(PPh3)2 primary aliphatic alcohols were oxidized cleanly to aldehydes, at room temperature the use of m-iodosylbenzoic acid instead of IOB considerably increased the yields for example, hexanal was formed from hexanol quantitatively (by GC) [19], Another catalytic system involved the use of simple lanthanide salts such as ytterbium triacetate [20]. Cyclic y-stannyl alcohols, readily available from cyclic vinyl ketones and Bu3SnLi, underwent oxidation accompanied by carbon-carbon bond cleavage (Grab fragmentation), when treated with IOB.BF3 and DCC. The products were unsaturated aldehydes or ketones. 

Although H NMR spectra of aryllead triacetates can be recorded in CDCI3 solution in the presence of tetra-methylsilane, cleavage of the methyl-silicon bond takes place when tetramethylsilane is treated with an aryllead(rv) tricarboxylate in trifluoroacetic acid.164 When the aryl moiety is substituted with an electron-withdrawing group, quantitative conversion of TMS was observed to give aryl(methyl)lead dicarboxylates 111, (Equation (136)) that were even isolated in two instances, although in modest to moderate yields 55% yield for the 4-fluorophenyl compound and 23% yield for the 4-trifluoroacetamidophenyl compound. 

Regeneration of the parent carbonyl compound from tosylhydrazones and 2,4-dinitrophenylhydrazones can be carried out in high yield using sodium nitrite in trifluoroacetic acid. Deprotection of tosylhydrazones using thallium triacetate in acetic add is also elficient. Oximes yield the carbonyl product on treatment with bromine in aqueous sodium bicarbonate, and the same conditions can be used to hydrolyse tosylhydrazones if HMPA is present. Aqueous nitric acid was found to be superior to both sulphuric and hydrochloric adds for the cleavage of the hydrazones (90) to the corresponding cyclohexanones. ... 

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