Oxidation using triphosgene

Materials and Purification. Chemicals were purchased from Aldrich chemical company and used as received unless otherwise noted 1,1,1,3,3,3-hexamethyl disilazane, ethylene glycol, triphosgene, poly(ethylene oxide) (MW = 600), poly(tetramethylene oxide) (MW = 1000), poly(caprolactonediol) (MW = 530), toluene diisocyanate (TDI), anhydrous ethanol (Barker Analyzed), L-lysine monohydride (Sigma) and methylene bis-4-phenyl isocyanate (MDI) (Kodak). Ethyl ether (Barker Analyzer), triethylamine and dimethyl acetamide were respectively dried with sodium, calcium hydride and barium oxide overnight, and then distilled. Thionyl chloride and diethylphosphite were distilled before use. 

Table 2.2. lists activators used less commonly for Moffatt oxidations. The following activators, namely diphosgene,262 triphosgene,263 2-chloro-1,3-dimethylimidazolinium chloride,264 l-cyclohexyl-3-(2-morpholinoethyl)-carbodiimide metho-p-toluenesulfonate,265 triphenylphosphine dibromide and dichloride,266 and phenyl dichlorophosphate,267 have been the subject of scientific monographs, in which they are proposed as suitable and convenient alternatives to more routinely used activators, and can offer improved oxidation conditions in some substrates. 

The preparation of 2,5-oxazolidinediones, the A -carboxy a-amino acid anhydrides, has received considerable attention, because of their usefulness in peptide chemistry. In a modification of a common route, A-Boc amino acids were reacted with triphosgene, followed by triethylamine <92JOC2755>. The products were obtained in 65-83% yield (Equation (31)). Oxidation of 1-arylvinyl carbamates (198) with lead tetraacetate proceeds through an oxazolone intermediate to afford 2,5-oxazolidinediones in moderate yield (Scheme 101) <90JOC1753>. 

TBS-protected lactaldehyde 689 is readily prepared with high enantiomeric purity by a mild oxidation of the propanol 688 under Swem-type conditions using bis(trichloromethyl)car-bonate (triphosgene)-DMSO [203]. Triphosgene is a white crystalline solid that is easily handled, and it is a safe alternative for such other DMSO activators as phosgene or diphosgene dimer. 

Based on the above findings, a new methodology was described for the synthesis of polymer-bound triphenylphosphine dichloride 1309 by the use of triphosgene [988, 989]. This type of resin has attracted a lot of attention due to the simplicity of separating the product from the resulting phosphine oxide [990]. 

The use of triphosgene as a DM SO activator has several advantages over oxalyl chloride. It is a solid that can be weighed accurately and is less susceptible to hydrolysis. Furthermore, the oxidation of yS-phenylethanols with triphosgene/DMSO gave better yields compared to oxidation with oxalyl chloride/DMSO or TFAA/ DMSO [1363]. 

Tab. 4.S1. Oxidation of alcohols using the triphosgene/DMSO system [1362],...

Table 4.52 compares the results obtained for the oxidation of alcohols with the triphosgene/DMSO reagent with those obtained using the traditional Swern method (oxalyl chloride/DMSO) [1363]. 

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