PDC in DMF

PDC in DMF is able to perform alcohol desilylation and in situ oxidation.136... 

Oxidation of the primary alcohol with PDC in DMF leads to a hydroxyacid that cyclizes ... 

Pyridinium dichromate (PDC) The problem caused by the acidic nature of PCC is largely removed by using the neutral reagent PDC . For example, geraniol (7.5) was oxidized to geranial (7.6) in 92% yield by PDC in DMF (dimethylformamide) solvent. 

But non-conjugate alcohols such as citronellol (7.7) on treatment with PDC in DMF give the corresponding acid 7.8 however, the aldehyde 7.9 is obtained with PDC in CH2CI2. 

In DMF solution, however, PDC oxidizes nonconjugated primary alcohols to the corresponding carboxylic acids.Oxidations of 2° alcohols by PDC in DMF proceed to give the corresponding ketones. 

Many of the oxidants employed to prepare aldehydes from primary alcohols may be used to further oxidize the aldehyde initially formed to the corresponding carboxylic acid. The most common oxidants for this purpose include KMn04," chromic acid, sodium chlorite,silver oxide," and PDC in DMF. °... 

Oxidation of a cyanohydrin derived from a conjugated aldehyde (as the O-TMS derivative) using py-ridinium dichromate (PDC) in DMF gave an a,p-unsaturated lactone (6 -butenolide) as the major product (equation 12). Simple nonconjugated cyanohydrins are not satisfactory substrates for the synthesis of acyl cyanides using PDC, because they seem to add to the initially formed acyl cyanides, leading ultimately to cyanohydrin esters. Oxidation of cyanohydrin to acyl cyanides can be carried out either by means of manganese dioxide, mthenium-catalyzed oxidation with r-butyl hydroperoxide or NBS. ... 

The first total synthesis of the nucleoside antibiotic herbicidin B was accomplished in the laboratory of A. Matsuda. The key step was a novel aldol-type C-glycosidation reaction promoted by Sml2 between a 1-phenylthio-2-ulose derivative and a 1- 3-D-xylosyladenine-5 -aldehyde derivative. During the preparation of the phenylthio sugar subunit, the Moffatt oxidation was applied to convert the primary alcohol to the corresponding aldehyde, which was immediately oxidized with PDC in DMF/MeOH to the methyl ester. The reaction conditions were completely compatible with the silyl protecting group as well as the thioacetal functionality. 

Compound 32 was prepared in four steps from 4-hydroxy-2-butanone (36). Protection of the alcohol ftmction of 36, as a tetrahydropyranyl (THP) ether 37, was acconqjlished with dihydropyran (DHP) and NH4CI catalyst in refluxing THF (24). Wittig reaction of 37 with the ylide from butyl(triphenyl)phosphonium bromide (n-BuLi, THF) resulted in alkylidenation to form 38, but the yield was less than 5%, even with dropwise addition of the ylide to the aldehyde at -78 . Removal of the THP group, followed by oxidation of the alcohol directly to the acid under neutral conditions (PDC in DMF, 33) afforded 32. Mild oxidation conditions are required to prevent migration of the double bond from the 3-position to the 2-position. 

Primary alcohols are oxidized by the easily prepared pyridinium dichromate [6] (PDC) in DMF (Eq. 6.3) [7] or by Jones reagent in acetone (Eq. 6.4) [8]. Secondary alcohols are also easily oxidized to ketones under these conditions. Potassium permanganate in aqueous NaOH will oxidize primary alcohols but is not selective, attacking alkene sites as well. 

RCHO — RCOOCHi. Aliphatic aldehydes can be converted directly to methyl esters by PDC (6 equiv.) and methanol in DMF in yields of 60-85%. The method is not useful in the case of aromatic aldehydes or of higher esters. 

The third-generation dendrimer palladium complex (31, containing 24 PdC groups) was applied in the Stille coupling of methyl-2-iodobenzoate with 2-(tributyl-stannyl)thiophene in DMF (Scheme 10 lmol% catalyst). In contrast to what was observed with the monomer (PPh3)2PdCl2, no palladium metal formation was... 

A2-Butenolides. A simple route to A2-butenolides from a,/5-enals involves conversion to the O-trimethylsilylcyanohydrin (cyanotrimethylsilane, 4, 542 -543 5, 720 722 6, 632 633), which is then oxidized by PDC (3 equivalents) in DMF. The sequence from geraniol is typical (equation I). 

Pyridinium dichromate (14) is an isolable, stable orange solid that can be simply and safely prepared. PDC had been used previously, but it was Corey and coworkers who demonstra the wide applicability of this mild and selective oxidant in organic synthesis. PDC is very soluble in solvents such as DMF, water and DMSO, but sparingly soluble in chlorinated hydrocarbons and acetone. It is normally used either as a solution in DMF or as a suspension in dichloromethane (Table 12). 

Primary and secondary allylic alcohols and saturated secondary alcohols are oxidized to the corresponding carbonyl compounds quickly and in high yield at room temperature in DMF. There is no appreciable overoxidation of allylic alcohols in DMF, but primary saturated alcohols are readily oxidized to their corresponding acids. Recently, it has been reported that aldehydes may be converted to methyl esters by oxidation with PDC in the presence of methanol. Preparation of other esters, or methyl esters direct from the alcohol, proved to be less efficient. 

QuinoUnium dichromate disfdays reverse selectivity to PDC in dichloromethane primary alcohols can be oxidized directly to acids, but in DMF the oxidation is selective for the preparation of aldehydes. 

Selective monoprotection of 1,4-butanediol (1.20) with TBDPSCl (terf-butyldiphenylsilyl chloride) (see Table 1.2) is another example of chemoselectivity. Monoprotected alcohol 1.21 on oxidation with PDC (pyridinium dichromate) in DMF (dimethylformamide) afforded the corresponding carboxylic acid derivative 1.22 in 75% yield. 

When used in DMF, PDC oxidizes aldehydes and primary alcohols to carboxylic acids. However, allylic primary and secondary alcohols are oxidized only to the a ,j3-unsaturated carbonyl compounds. All these oxidations proceed in high jrield. 

Unlike lithium halides, tetrabutylammonium halides are fully dissociated in PDC, but they are associated in HMPA, and this is in agreement with simple electrostatic considerations. Similar results have been found in DMF, where alkali metal halides are fully dissociated whereas tetraaUcylammonium halides are associated 56, 57). 

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