Polymeric reagents, oxidation with

Polymeric reagents, oxidation with, 99 Potassium cyanide, 20 L Proline, N bcnzyloxycarbonyl-3-hydroxy-[1,2-Pyrrohdinedicarboxyhc acid, 3-hydroxy, 1 (phenylmcthyl) ester], 89 L Proline, N trifluoroacetyl [2-Pyrrohdine-carboxylic acid, 1 (trifluoroacetyl), (5)-], 125... 

Platinum anode, 57, 92 Polymeric reagents, oxidation with, 56,99 Potassium amide, 57, 42 Potassium tert butoxide, 55, 12, 13, 57, 8, 45,84... 

Polymer-supported /eagent. Italian chemists have prepared a supported form of this oxidant by reaction of the Cl" form of an anion exchange resin (Anibcriyst A-26, Amberlyst A-29, Amberlite IRA 400, or Ainberlite 904) in llaO with chromium trioxide to obtain a CrOaH" form of the resin. This polymeric reagent oxidizes primary and secondary alcohols in high yield (usually 85-957o). The chloride form of the resin is regenerated by wash with NaOH and HCI solutions. 

Several solid supports have been employed for the attachment of o-iodosobenzoic acid, including silica gel, titania and nylon [89]. Two polymer-supported o-iodoxybenzoic acid reagents have recently been reported. The first was obtained by attaching a carboxymethyloxy derivative of f-butyl o-iodo-benzoate to an aminopropylated silica gel and oxidation with oxone [90]. The second involved chloromethylated polystyrene which was coupled with methyl 5-hydroxy-2-iodobenzoate and eventually oxidized by Bu4NS05H/MeS03H [91]. Some of these polymeric reagents appear in Scheme 31. 

The alkylation of different polymeric reagents 268 (prepared from the corresponding odorless 1,3-dithiols and aldehydes) has been performed by successive deprotonation with n-BuLi and reaction with alkyl bromides and iodides. Final oxidation with periodic acid or with mercury(II) perchlorate gave the corresponding ketones (Scheme 73)452. 

The Amberlyst A-26 resin consists of a complex hydrocarbon network with cationic ammonium ion appendages that serve as counterions to the anionic chromium oxidant, HCr04". Heating the insoluble polymeric reagent with an alcohol results in oxidation to a carbonyl compound, with formation of an insoluble Cr by-product. Not only can the metal by-product be removed by filtration without added solvent, it can also be regenerated and reused in a subsequent reaction. 

A silver dichromate complex with poly(ethyleneimine) has been used to oxidize benzyl alcohol in toluene to ben-zaldehyde in 98% yield.199 The polymeric reagent could be regenerated several times with no loss in activity. No... 

N-oxide salts (HBTU and TBTU, respectively) [39], or from l-hydroxy-7-azabenzotriazole (HOAt) such as N-[(dimethylamino)-lH-l,2,3-triazolo[4,5-fe] pyridino-l-y]methylene]-N-methy]methanaminium tetrafluoroborate N-oxide (HATU) [40], are well established reagents. They are especially devoted to peptide coupling reactions due to their efficiency and the low degree of undesirable race-mization produced in the final peptide compared to the use of classical carbodi-imide-coupling methods. Therefore, as the polystyrene-supported HOBt is an often used polymeric reagent (Section 7.6.3) [41], its transformation in a supported HOBt and tetramethylurea-derived aminium salt analog to HBTU and TBTU resulted directly. Thus, the reaction of polystyrene-2% divinylbenzene copolymer resin P-HOBt (20) with tetramethylchloroformamidinium tetrafluoroborate (21) (4 equivalents) in the presence of triethylamine gave polymeric N-[(lH-benzotriazol-l-yl)(dimethylamino)methylene]-N-methylmethanaminium tetrafluoroborate N-oxide (P-TBTU, 22) (Scheme 7.6) [42],... 

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