Group cleavage, reductive

Osmium tetroxide used in combination with sodium periodate can also effect alkene cleavage.191 Successful oxidative cleavage of double bonds using ruthenium tetroxide and sodium periodate has also been reported.192 In these procedures the osmium or ruthenium can be used in substoichiometric amounts because the periodate reoxidizes the metal to the tetroxide state. Entries 1 to 4 in Scheme 12.18 are examples of these procedures. Entries 5 and 6 show reactions carried out in the course of multistep syntheses. The reaction in Entry 5 followed a 5-exo radical cyclization and served to excise an extraneous carbon. The reaction in Entry 6 followed introduction of the allyl group by enolate alkylation. The aldehyde group in the product was used to introduce an amino group by reductive alkylation (see Section 5.3.1.2). 

Reduction of Sulfonamides Cyclization Promoted by Af-Tosyl Group Cleavage... 

Furthermore unsaturated aldehydes can be obtained by the reaction of 12 with e. g. cyclohexane carboxylic acid chloride, subsequent alkaline cleavage of the remaining silyl grouping and reduction with sodium borohydride give 3-hydroxy-3-cyclohexyl-1,1-dimethoxypropane (54) which yields 3-cyclohexyl-acrolein (JJ)51 via acid treatment under dehydratation. 

To facilitate sequencing analysis and enzymatic cleavage, reduction and alkylation of the peptides to open their potential disulfide bridges is recommended. Several alkyl groups can be used acrylamide, iodoacetamide, and 4-vinylpyridine (4-VP). S-pyridylethylation is preferred over the other alkyl groups when Edman degradation (PTH-4-pyridylethylated-Cys is commercially available) and MS (addition of 57 Da per alkylated cysteine residue) have to be performed. 

Kemp, D.S. and Reczek, J. (1977) New protective groups for peptide synthesis. III. The Maq ester group. Mild reductive cleavage of 2-acyloxymethyleneanthra-quinones. Tetrahedron Letters, 18, 1031-1034. 

The electrocatalytic mechanism of the reduction of 2-nitro- and 4-nitroimidazole [948, 949] and 3-nitro-1,2,4-triazole [950] on gold (Au) potential deposition electrode proceeds through chemisorption of the nitro group and reductive cleavage of one of the two N-0 bonds and gives diffusion-controlled limiting currents. 

During model studies directed towards the synthesis of the Mycalamides, Hoffmann and co-workers 41 discovered a reduction reaction which accompanied the deprotection of an /V-SEM derivative [Scheme 8.152]. Treatment of 152 1 with TT1AF in DMPU at 45 returned the a-hydroxy amide 152 2 as a 3 1 mixture of diastereoisomers. The authors speculate that the reduction reaction was caused by a reagent of the type N-CH2-0 or F-CH2-0 derived from cleavage of the SEM group. The reduction was a welcome and useful surprise since the nascent hydroxyl group is present in the natural product. 

The mitomycins (191) have attracted much attention as a result of their interesting structure and potent anticancer properties [43]. One approach to these materials is illustrated in Eq. 36 [44]. A key intermediate in the implementation of this plan is azocinone (193), a substance that proved accessible in high yield via the novel mediated A-tosyl group cleavage-cyclization-fragmentation of 194. Here, ascorbic acid behaves as a proton donor and a reductant in combination with anthracene (Scheme 17). 

If the amino group is to the carbonyl group, a reduction takes place at the carbonyl group rather than resulting in a cleavage of the carbon-nitrogen bond the polarographic... 

Desulfonylation. Various sulfonyl groups are reductively removed by Mg/MeOH. These include alkenyl sulfones, alkyl tosylates, and A -Boc-arenesulfonamides (p-toluenesulfonhydrazides, V-tosylaziridines ). But when the V-tosylaziridine contains an electron-withdrawing group, ring cleavage to give p-(V-tosylamino) derivatives takes precedence to detosylation. ... 

Desulfurative alkylations. Sulfides in which the a-carbon is substituted with an electron-withdrawing group undergo reductive cleavage by EtjGeNa. The organogermanium intermediates are reactive toward carbonyl compounds and allylic halides. ... 

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